Note: This feature might not be available on all editions of HelpNDoc. Check HelpNDoc's feature comparison page to learn more.
Word and PDF documents can be signed using an invisible signing certificate. Viewer applications such as Microsoft Word, Adobe Reader... check that a signed document is coming from the advertised author and that it hasn't been altered in any ways since it has been signed. HelpNDoc supports CER, PEM and PFX encoded certificates.
For more specific details, see: