> For the complete documentation index, see [llms.txt](https://docs.facephi.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.facephi.com/docs.facephi-en/rest-api/identity-api/identity-api-reference/digital-signatures.md).

# Digital Signatures

The Digital Signatures API allows adding globally trusted digital signatures and timestamps to PDF documents without the need for specialized hardware such as USB tokens or HSMs.

#### Features

* **PKI-based digital signatures**: Use of signatures based on certificates from trusted public CAs
* **Long-term validation (LTV)**: Signatures remain valid even after certificate expiration or revocation
* **Hardware security**: Keys stored in FIPS-compliant cloud HSMs
* **Handwritten signature support**: Optionally include visual handwritten signatures
* **Compatible with Adobe and Microsoft**: Fully compatible with Adobe Acrobat and Microsoft Office products