смысл всей статьи имхо можно выразить одним абзацем оттуда:
To sign an OpenOffice.org document using the created certificate, choose File -> Digital Signatures, press the Add button, select your certificate, and press OK to close the dialogs and sign the document. You should see a tiny Seal icon in the Status bar, which indicates that the document has now been digitally signed. Other users can view the certificate by double-clicking on the Seal icon and pressing the View Certificate button.