[iTextSharp] iTextSharp encryption options for PDF document

iTextSharp encryption options for PDF document (setEncryption)

The userPassword and the ownerPassword can be Nothing or have zero length. In this case the ownerPassword is replaced by a random string.

The open permissions for the document can be following:
AllowPrinting, AllowModifyContents, AllowCopy, AllowModifyAnnotations, AllowFillIn, AllowScreenReaders, AllowAssembly, and AllowDegradedPrinting

Easy way to choose which permission to use (VS2008 intellisense):
e.g. PdfWriter.AllowPrinting

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