> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/web/digital-signature/signature.md).
# JavaScript PDF Digital Signature Library
Secure digital documents with ease using the JavaScript PDF Digital Signature Library. Ensure authentication, integrity, and non-repudiation for your digital signatures on web. The Apryse Web SDK stre
{% hint style="info" %}
**Requirements**
*These packages are required to use these features in production. Trial keys have unlimited access to all features*
Package: Digital SignatureLive demo
{% endhint %}
Digital Signatures can be considered as the electronic equivalent of a physical signature with ink on paper. However an electronic signature also provides certain advantages over an ink-and-paper signature. It can secure and protect a digital document by creating a signing fingerprint uniquely identifying a sender. The recipient of the document and signature confidence of the sender's identity validates that the document has not been altered by anyone else since it was signed.
Some of these main advantages are:
**Authentication** A digital signature allows precise identification of who created/signed a document. It can be safely assumed that when a signature is valid, you know who signed it.
**Integrity** A digital signature allows users to easily validate whether the contents of a document were changed after it was signed.
**Non-repudiation** A digital signature ensures that the signer cannot deny that they signed the document.
Apryse SDK benefits include:
* Import signature fields via XFDF/FDF
* Export signature data via XFDF/FDF
* Built-in support for PKI signing (and PFX digital certificates)
* Support for custom signature handlers
* Sign with images, ink annotations, or entirely custom appearances
## How does a Digital Signature work?
A [digital signature](https://en.wikipedia.org/wiki/Digital_signature) will generate a unique value (hash / digest) from the combination of the document data and [private key](https://en.wikipedia.org/wiki/Public-key_cryptography). During verification, the document data and [public key](https://en.wikipedia.org/wiki/Public-key_cryptography) is used to generate the exact same unique value (hash / digest). If these unique values match then we can say the data has not been altered and the digital signature is valid.
## Digital Signature vs e-Signature
An e-signature is an annotation that appears in the document but has no additional identifiable information about the creator other than an author field which can be altered.
A digital signature on the other hand uses a cryptographic algorithm to uniquely identify the author and any alterations to the document including the annotations or e-signature would result in an invalid digital signature validation.
## Certificate Authority (CA)
A cryptographic digital signature can use a [certificate authority](https://en.wikipedia.org/wiki/Certificate_authority) (CA) to act as a trusted third party between a sender and other parties.
### How does a CA work?
The CA will issue a [digital certificate](https://en.wikipedia.org/wiki/Public_key_certificate) which contains a public key and the identity of the owner. A matching private key is not made available publicly, but kept secret by the end user who generated the key pair. The certificate is also a confirmation or validation by the CA that the public key contained in the certificate belongs to the person, organization, server or other entity noted in the certificate. A CA's obligation in such schemes is to verify an applicant's credentials, so that users and relying parties can trust the information in the CA's certificates. CAs use a variety of standards and tests to check this information. In essence, the certificate authority is responsible for saying "yes, this person is who they say they are, and we, the CA, certify that".
### How does a digital signature and a CA work together?
For security and legal purposes, a public key owner must be verifiable and it is common to use a [public key infrastructure](https://en.wikipedia.org/wiki/Public_key_infrastructure) (PKI) where the public key owner is validated by a CA. Since a public key is used to validate a cryptographic signature then a digital signature and a CA work together to authenticate the owner and the data.
### Is a CA required for digital signatures?
No. The CA is required in use cases where a third party entity needs to be involved between a sender and other parties. If a CA is not used then a digital signature can instead use a self-signed certificate as shown in our [digital signature sample](/web/get-started/samples/digitalsignaturestest.md) or [webviewer digital signature demo](https://showcase.apryse.com/digital-signatures) for example. Apryse does not provide CA services so it is the responsibility of users creating a digital signature workflow to use a CA if it is required for your use cases.
## Digital Signature Security Features
### Certificate Expiration vs Certificate Revocation
A document that has been signed using a certificate without any additional features (such as Document Timestamping (DTS) or Long Term Validation (LTV)) will result in the signature eventually expiring, as every certificate has an expiry date when they are generated.
This is different from when Certificate Revocation occurs, a process by which a certificate is deemed invalid *before* the end of its lifecycle. The revocation can occur for one of many reasons, as outlined in [RFC 5280 Section 5.3.1](https://tools.ietf.org/html/rfc5280#section-5.3.1). When revocation of a certificate occurs, it is placed on a [Certificate Revocation List (CRL)](https://en.wikipedia.org/wiki/Certificate_revocation_list).
This behavior of expiration and revocation ensures that digital signatures placed on documents are only valid for a set period of time, either prior to the expiration date of the signature(s), or if the signature(s) have not been revoked at the time the document is viewed
### Document Timestamping (DTS)
Should the validity of the signature(s) need to be maintained outside of the certificate expiration timeframe and/or even if the certificates have been revoked, then [Document Timestamping](/core/digital-signature/dts.md#about-doctimestamp-dts) will ensure any applications that validate the signatures will check if the certificate was valid at the secure time (i.e. timestamp) of the certificate as certified by a third party trust provider (i.e. Certificate Authority).
### Long Term Validation (LTV)
Should the signature(s) need to be validated for an extended period of time for archival purposes, then Long Term Validation (LTV) should be applied to the signature to ensure that even if a CAs CRL responder is no longer active, an application can still validate the signature(s) based on the time they were applied.
It is worth noting that DTS is often applied alongside LTV, but note that they are two separate features.
## Signature tool
WebViewer's JavaScript PDF library has a built in signature tool that lets users create signature annotations. In fact, signature annotations are just freehand annotations, or ink annotations according to the PDF specification. With WebViewer, it is possible to preview signatures, save signatures and apply default signatures directly.
Digital signatures are also supported in WebViewer, meaning that you can digitally sign and certify a PDF document. You can see more in the [digital signature guide](/web/digital-signature/sign-pdf.md) and the [advanced digital signature sample](/web/get-started/samples/digitalsignaturestest.md).
One significant difference between digital signatures and signature annotations is that digital signatures employ asymmetric cryptography and provide an extra layer of security whereas signature annotations are just created superficially and can move around the document.
## Sign App Sample
Sign App demonstrates building a signing application where users can request signatures on the documents by placing fields, sign documents, review signed documents using Apryse PDF SDK.
{% embed url="" %}
To speed up development and time to market we provide full source code on the [GitHub repo](https://github.com/ApryseSDK/pdftron-sign-app/).
## Demo
[Digital Signature Demo](https://showcase.apryse.com/digital-signatures)
## Get started
[Sign app sample](https://github.com/ApryseSDK/pdftron-sign-app/) Build a signing application that leverages Apryse, React-Redux and Firebase.
[Signature tool](/web/digital-signature/signature-tool.md) To utilize the built-in signature tool for signature creation.
[Interact with signature form field](/web/digital-signature/interacting-with-signature-field.md) To use a signature form field to utilize the signature tool or APIs.
[Sign a PDF Document](/web/digital-signature/sign-pdf.md) To digitally sign a PDF document
[Certify a PDF Document](/web/digital-signature/certify-pdf.md) To certify a PDF document
[Verify a PDF Document](/web/digital-signature/verify-pdf.md)
[Custom Signing](/web/digital-signature/custom-signing.md)
[Embedded Timestamping](/web/digital-signature/emb-tst.md)
## Related blogs
[Ultimate Guide to Digital Signatures](https://apryse.com/blog/digital-signatures-guide) - 6/28/23
[How to Support Multiple Digital Signatures in a Single Document in JavaScript with Apryse SDK](https://apryse.com/blog/multiple-digital-signature-on-one-document) - 8/24/23
["Signature" Signatures - Custom Signing Made Easy](https://apryse.com/blog/webviewer/create-easy-custom-signature-workflows) - 9/29/22
[Enhancing Digital Signature Security with Secure-by-Default Verification plus MDP](https://apryse.com/blog/digital-signature/secure-by-default-verification) - 9/21/20
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