This article covers how to install and configure digitally sign for OpenOffice.org.
From the article:
The ability to digitally sign OpenOffice.org documents is a boon for users who want to make their document exchange and collaboration secure. Using digital signatures in OpenOffice.org is not that difficult, but configuring it involves several steps that are far from obvious.
Before you enable the digital signatures feature in OpenOffice.org, you must obtain a digital certificate and install it on your machine. A digital certificate is a password-protected file that includes a variety of information, including the name and email address of the certificate owner, encryption key, issuing authority, and expiration period. Digital certificates are normally issued by so-called certificate authorities. Most certificate authorities charge for certificates, but not all do. CACert is a community-driven certificate authority that issues perfectly usable certificates free of charge.