> 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 you to add 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