From veridis: Digitally sign (authenticate) your PDF files in Adobe Acrobat Professional using PGP Key. A signed PDF document allows the reader of this document to verify this signature and to be sure that the document has not been altered during its transfer. It also allows the reader to know for sure who is the author of the PDF document. FileCrypt Acrobat Pro can generate a PGP key if you don't have one.
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