Moving beyond physical formats and establishing a paperless workflow is an essential requirement for business efficiency. To take this step with full confidence, mastering how to sign a PDF document with a digital signature is crucial: it is the only way to ensure the integrity, authenticity, and non-repudiation of any binding agreement. This technological adoption not only drastically accelerates contracting cycles but, backed by advanced cryptography and strict regulatory frameworks, provides legal certainty far superior to that of the traditional handwritten signature.
\nThis article breaks down, step by step, the legal aspects, essential technical requirements, and best practices for successfully implementing an online digital signature, highlighting how advanced solutions like Tecalis are completely redefining the contractual landscape.
","strapi_component":"blog.content-rich-text"},{"id":1075,"name":null,"description":"Sign a PDF document with a digital signature for free
","button":"Try Tecalis Sign","url":"https://www.tecalis.com/products/electronic-signature","blank":true,"image":null,"strapi_component":"blog.cta"},{"id":4452,"text":"The digitization of signing processes has transformed the way companies interact with customers, suppliers, and employees, making digital signatures in PDFs a cornerstone in environments where agility and legal certainty are non-negotiable. Unlike paper, which is vulnerable to forgery, alteration, or loss and relies on costly handwriting analysis in cases of repudiation, the electronic signature is secured through asymmetric cryptography.
\nThis guarantees the document’s absolute integrity: if a single bit is altered after signing, the cryptographic hash breaks instantly, revealing the tampering. Furthermore, as it is validated by Trust Service Providers (under regulations such as eIDAS), an advanced biometric signature possesses probative value equivalent to or greater than that of a handwritten signature, ensuring unparalleled technical traceability thanks to qualified time stamps and detailed logging of all actions.
\nThis technological leap not only provides legal robustness but also drives business transformation through three key advantages:
\n| Feature | \nPaper Signature (Handwritten) | \nDigital Signature on PDF | \n
|---|---|---|
| Document Integrity | \nVulnerable to alterations or page substitution. | \nThe cryptographic hash is broken if a single bit is altered after signing. | \n
| Signatory Identity | \nRequires handwriting analysis in case of repudiation. | \nValidated by a Trust Service Provider (eIDAS). | \n
| Traceability | \nLimited to the physical medium. | \nQualified time stamp and audit trail. | \n
| Cost and Time | \nHigh (printing, courier service, physical storage). | \nLow (instantaneous, global, cloud storage). | \n
The use of digital certificates and electronic signature platforms spans virtually every department within an organization:
\nThe electronic signature has established itself as a cross-functional and indispensable tool for the entire organization. Its implementation automates and ensures the full legal validity of critical workflows across all areas, from employment agreements in Human Resources and contracts in Sales to notarial and medical documents.
","color":"default","strapi_component":"blog.callout"},{"id":4454,"text":"For the process to be fully valid, simply pasting a scanned image of a signature is not enough, as this lacks strong legal evidentiary value. It is essential to use platforms that comply with current regulations and are tailored to the risk level of each transaction. At the most basic level is the simple electronic signature, a streamlined method that is useful and sufficient for low-risk internal processes, such as reading and accepting corporate policies.
\nFor 90% of commercial and labor agreements, it is most advisable to use the Advanced Electronic Signature (whether biometric or via OTP or a one-time password). This level uniquely binds the signer, allows for their irrefutable identification, and guarantees that the document has not been altered. Additionally, the use of biometrics adds an invaluable forensic layer in the event of legal disputes.
\nFinally, for the most critical and high-risk transactions, Advanced Electronic Signature + KYC verification should be used. This method requires signing the PDF with a reliable identity verification process. Its greatest strength lies in the fact that it carries a presumption of full validity, being legally equivalent to a handwritten signature without the need to provide any prior expert evidence in the event of repudiation.
","strapi_component":"blog.content-rich-text"},{"id":4455,"text":"The unequivocal answer is yes. The validity of digital signatures, both online and offline, is safeguarded by a strict and unified regulatory framework across Europe. The eIDAS Regulation establishes a common standard for electronic signatures throughout the European Union. This regulation ensures the interoperability and mutual recognition of digital identities. In Spain, this regulation is supplemented by Law 6/2020 of November 11, which regulates certain aspects of trusted electronic services. The cornerstone of this framework is the principle of non-discrimination: a signature shall never be denied legal effect or admissibility as evidence in a trial merely because it is in electronic format. This evidentiary validity becomes even stronger in the event of a legal dispute, where the burden of proof depends on the level of security employed; in the case of an advanced biometric signature, the law automatically presumes its authenticity and integrity, placing the burden of proof on the opposing party attempting to repudiate it to demonstrate that it is invalid.
\nMeanwhile, when using an advanced signature, the legal strength lies in the Evidential Document generated by the provider platform. This technical document constitutes a robust body of evidence for any judge by collecting irrefutable electronic evidence: IP addresses, geolocation, SHA-256 hashes of the documents, OTP codes via SMS, and the timestamp from a Time Stamping Authority.
","strapi_component":"blog.content-rich-text"},{"id":1076,"name":null,"description":"What type of electronic signature do you need? Learn about the different types and their legal validity in this guide
","button":"Download free guide","url":"https://www.tecalis.com/electronic-signature-types-guide-levels-sending-format-simple-advanced-qualified-biometric","blank":true,"image":null,"strapi_component":"blog.cta"},{"id":4456,"text":"To ensure that a digitally signed PDF document is unassailable from both a technical and legal standpoint, very specific requirements based on the European PAdES standard must be met. These are the fundamental pillars that guarantee maximum security:
\nFinally, to ensure the file’s legal durability, long-term validation must be applied. This process involves embedding the certificate revocation status (OCSP or CRL) within the PDF itself at the time of signing, ensuring that the document can be validated without issues 10, 20, or even 50 years later, even if the original issuing authority no longer exists.
","strapi_component":"blog.content-rich-text"},{"id":963,"title":null,"alt":"Person managing a digital signature from their laptop.","figcaption":null,"link":null,"blank":null,"image":{"id":5147,"name":"firma_digital_interior_1.png","hash":"firma_digital_interior_1_eafe01bba7","sha256":null,"ext":".png","mime":"image/png","size":897.3,"url":"/uploads/firma_digital_interior_1_eafe01bba7.png","provider":"local","provider_metadata":null,"created_at":"2026-05-06T10:30:18.000Z","updated_at":"2026-05-06T10:30:18.000Z","alternativeText":"","caption":"","width":954,"height":525,"formats":{"thumbnail":{"name":"thumbnail_firma_digital_interior_1.png","hash":"thumbnail_firma_digital_interior_1_eafe01bba7","ext":".png","mime":"image/png","width":245,"height":135,"size":96.94,"path":null,"url":"/uploads/thumbnail_firma_digital_interior_1_eafe01bba7.png"},"medium":{"name":"medium_firma_digital_interior_1.png","hash":"medium_firma_digital_interior_1_eafe01bba7","ext":".png","mime":"image/png","width":750,"height":413,"size":868.97,"path":null,"url":"/uploads/medium_firma_digital_interior_1_eafe01bba7.png"},"small":{"name":"small_firma_digital_interior_1.png","hash":"small_firma_digital_interior_1_eafe01bba7","ext":".png","mime":"image/png","width":500,"height":275,"size":385.58,"path":null,"url":"/uploads/small_firma_digital_interior_1_eafe01bba7.png"}},"previewUrl":null,"localFile___NODE":"822d6738-7f9d-538e-9e32-c4271faacbef"},"strapi_component":"blog.image"},{"id":4457,"text":"Signing a PDF document with a digital certificate requires a specific technical procedure. You can use a certificate installed on your computer, a USB token, or a cryptographic card. To do this, it is common to use industry-standard software such as Adobe Acrobat Reader. This process applies the electronic identity securely and with full validity. Additionally, it guarantees the file’s integrity. To achieve this, it uses the operating system’s certificate store (Windows or macOS). Finally, it embeds the credentials into the document’s internal structure without the need for external platforms.
\nTo complete this process correctly, follow these steps:
\nKnowing how to verify a digital signature in a PDF is just as crucial as the act of signing itself. Receiving a signed document has no practical or legal value if its absolute authenticity and integrity cannot be immediately verified.
\nWhen opening the file in compatible readers such as Adobe Acrobat, the software performs an automatic data check. To review the details manually, simply access the Signatures Panel by clicking the pen-shaped icon located in the left-hand side menu.
\nWithin this panel, the validation status is displayed through three visual indicators that determine the file’s integrity. A green checkmark confirms that the signature is valid, the document has not been altered, and the certificate is backed by trusted lists such as the AATL (Adobe Approved Trust List) or EUTL (European Union Trust List). Meanwhile, a yellow triangle warns that, although the signature is correct, the root certificate is not trusted on that specific device (a common situation with self-signed certificates). Finally, a red cross (X) represents a critical alert indicating that the certificate is completely invalid or, in the worst-case scenario, that the text has been tampered with. To ensure the detection of such subsequent alterations, the PAdES standard operates as follows:
\nKnowing how to verify a digital signature is just as crucial as signing it to ensure the document’s authenticity and integrity. Competent readers perform automatic checks using visual status indicators, while the PAdES standard secures the file by structuring it into immutable layers that track any subsequent alterations.
","color":"default","strapi_component":"blog.callout"},{"id":964,"title":null,"alt":"Mobile screen displaying a digital signature made with Tecalis Sign.","figcaption":null,"link":null,"blank":null,"image":{"id":5148,"name":"firma-digital-interior-2.png","hash":"firma_digital_interior_2_e74a23c709","sha256":null,"ext":".png","mime":"image/png","size":783.9,"url":"/uploads/firma_digital_interior_2_e74a23c709.png","provider":"local","provider_metadata":null,"created_at":"2026-05-06T10:32:50.000Z","updated_at":"2026-05-06T10:32:50.000Z","alternativeText":"","caption":"","width":954,"height":525,"formats":{"thumbnail":{"name":"thumbnail_firma-digital-interior-2.png","hash":"thumbnail_firma_digital_interior_2_e74a23c709","ext":".png","mime":"image/png","width":245,"height":135,"size":91.91,"path":null,"url":"/uploads/thumbnail_firma_digital_interior_2_e74a23c709.png"},"medium":{"name":"medium_firma-digital-interior-2.png","hash":"medium_firma_digital_interior_2_e74a23c709","ext":".png","mime":"image/png","width":750,"height":413,"size":809.19,"path":null,"url":"/uploads/medium_firma_digital_interior_2_e74a23c709.png"},"small":{"name":"small_firma-digital-interior-2.png","hash":"small_firma_digital_interior_2_e74a23c709","ext":".png","mime":"image/png","width":500,"height":275,"size":363.62,"path":null,"url":"/uploads/small_firma_digital_interior_2_e74a23c709.png"}},"previewUrl":null,"localFile___NODE":"3e578082-7a32-5b9a-b0bb-ae488067894f"},"strapi_component":"blog.image"},{"id":4459,"text":"For organizations, relying on every customer to have a digital certificate installed creates unacceptable friction. This requirement often leads to abandonment during the conversion and signing of contracts. Current best practices dictate the use of integrated cloud platforms. These solutions simplify the end-to-end process and guarantee full legal validity. Adopting this technological approach allows companies to streamline their workflows. Additionally, it improves the customer experience and ensures regulatory compliance. To achieve this perfect balance between agility and legality, the following strategies are recommended:
\nWhen choosing a technology partner to meet the need for digitally signing a PDF document, Tecalis Sign stands out as one of the most advanced and reliable solutions in Europe and globally. Unlike generic alternatives, this suite stands out for its native compliance with the eIDAS Regulation, ensuring that every signature—whether advanced, biometric, or KYC-based—has indisputable legal standing in any court. This ensures that corporate processes not only gain in agility but also operate under the umbrella of the strictest European regulations regarding trust services and document integrity.
\nIts technical superiority is evident in a robust approach to security and identity verification. Rather than simply sending an email, the solution integrates AI-driven KYC processes to confirm the true identity of the person behind the screen before allowing them to sign. Additionally, by employing advanced biometric technology, it captures unique parameters such as pressure, speed, and stroke acceleration. This sensitive data is protected by asymmetric encryption in strict compliance with the GDPR, so that only a judge or notary holds the key to decrypt it in the event of a dispute. All of this, combined with blockchain-backed traceability, generates a comprehensive evidentiary document that safeguards the principle of non-repudiation.
\nFinally, the platform successfully combines this extremely high level of legal security with a user experience characterized by multi-channel access and a completely frictionless process. With Tecalis Sign, companies can send PDF documents for signature through everyday channels such as SMS, WhatsApp, or email. This allows customers to formalize legal and binding contracts in less than a minute directly from any smartphone. By eliminating the need to install third-party apps or have digital certificates pre-installed on the user’s device, conversion rates are optimized, and agreements are closed quickly and 100% securely.
","strapi_component":"blog.content-rich-text"},{"id":4461,"text":"Is an electronic signature the same as a digital signature?
\nAlthough they are used as synonyms, technically they are not the same. An electronic signature is the broad legal concept (data in electronic format attached to other electronic data that the signer uses to sign). A digital signature is the underlying technology (mathematical algorithms and public-key cryptography) used to implement a secure, advanced, or KYC-compliant electronic signature.
\nWhat happens if the digital certificate I used to sign the PDF expires?
\nIf the document was signed using software or a platform that applied a Qualified Time Stamp and Long-Term Validation policies, the signature will retain its legal validity indefinitely, as it is certified that at the exact moment the signature was made, the certificate was valid and intact.
\nCan a PDF be signed from a mobile phone?
\nYes. Through eIDAS cloud platforms such as Tecalis, the recipient receives a link via SMS or email. Upon clicking, they view the PDF adapted to their smartphone screen, enter a security OTP code or draw their biometric signature, and the platform handles all cryptographic sealing on the cloud servers, returning the final signed PDF to both parties.
","strapi_component":"blog.content-rich-text"},{"id":2,"title":"Glossary of Terms","list":"Do you want to sign documents online securely, with eIDAS certification and full traceability?
","button":"Contact us","url":"https://www.tecalis.com/contact","blank":true,"image":null,"strapi_component":"blog.cta"}],"blog_categories":[{"id":13,"name":"Electronic Signature","url":"electronic-signature"},{"id":23,"name":"Digital Transformation","url":"digital-transformation"},{"id":15,"name":"Legal Framework ","url":"regulatory-legal-framework"}],"reading_time":"Reading time: 5 minutes."},"site":{"siteMetadata":{"title":"Tecalis","twitterHandle":"Tecalis"}}},"pageContext":{"id":"Blog-posts_416","title":"How to Sign a PDF Document with a Digital Signature: Fast and Legal","langKey":"en","location":"https://tecalis.com/blog/how-to-sign-a-pdf-document-with-a-digital-signature","dateFormat":"MMMM D, YYYY","translates":{"en":"/blog/how-to-sign-a-pdf-document-with-a-digital-signature","es":"/es/blog/como-firmar-documento-pdf-firma-digital"},"images":{"3e578082-7a32-5b9a-b0bb-ae488067894f":{"data":{"image":{"childImageSharp":{"gatsbyImageData":{"layout":"constrained","placeholder":{"fallback":"data:image/png;base64,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"},"images":{"fallback":{"src":"/static/216c91ae824deae12c496e2b236c6cd5/59ffd/firma_digital_interior_2_e74a23c709.webp","srcSet":"/static/216c91ae824deae12c496e2b236c6cd5/7b6bd/firma_digital_interior_2_e74a23c709.webp 350w,\n/static/216c91ae824deae12c496e2b236c6cd5/aa5f2/firma_digital_interior_2_e74a23c709.webp 512w,\n/static/216c91ae824deae12c496e2b236c6cd5/806ca/firma_digital_interior_2_e74a23c709.webp 520w,\n/static/216c91ae824deae12c496e2b236c6cd5/59ffd/firma_digital_interior_2_e74a23c709.webp 572w","sizes":"(min-width: 572px) 572px, 100vw"},"sources":[]},"width":572,"height":315}}}}},"822d6738-7f9d-538e-9e32-c4271faacbef":{"data":{"image":{"childImageSharp":{"gatsbyImageData":{"layout":"constrained","placeholder":{"fallback":"data:image/png;base64,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"},"images":{"fallback":{"src":"/static/e0421c4bb0cc3fc4df33f652075b3a12/59ffd/firma_digital_interior_1_eafe01bba7.webp","srcSet":"/static/e0421c4bb0cc3fc4df33f652075b3a12/7b6bd/firma_digital_interior_1_eafe01bba7.webp 350w,\n/static/e0421c4bb0cc3fc4df33f652075b3a12/aa5f2/firma_digital_interior_1_eafe01bba7.webp 512w,\n/static/e0421c4bb0cc3fc4df33f652075b3a12/806ca/firma_digital_interior_1_eafe01bba7.webp 520w,\n/static/e0421c4bb0cc3fc4df33f652075b3a12/59ffd/firma_digital_interior_1_eafe01bba7.webp 572w","sizes":"(min-width: 572px) 572px, 100vw"},"sources":[]},"width":572,"height":315}}}}}},"advertisements":{},"advertisementsForms":{},"ctas":{},"videos":{},"cookies":true}}, "staticQueryHashes": ["1208480927","235538228","2927780632","3803179178","536423426","63159454"]}