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PDF: Sign encrypted PDF document
To sign the encrypted document you need to set TElPDFDocument.DecryptionMode property to dmSign before opening the document with TElPDFDocument.Open() method.
After opening the document you need to check if the document is encrypted, set password/certificate for decryption and call Decrypt() method. In this case a document would be partially decrypted, and encryption would not be removed. After that you can sign the document.
If the document is not encrypted, TElPDFDocument.DecryptionMode property won't have any effect.
