blueghost, LibreOffice supports digital signatures via GnuPG for OpenDocument Format (ODF) files.
Digital Signature: https://en.wikipedia.org/wiki/Digital_signature
GnuPG: https://mastodon.online/@blueghost/111974048270035570
ODF: https://mastodon.online/@blueghost/111936020896554127Select: File > Digital Signatures > Digital Signatures > Sign Document > Select Certificate > Sign > Enter Password > OK > Close
A banner will appear stating the document is digitally signed.
Website: https://www.libreoffice.org
Mastodon: @libreoffice