.NET IOException (Invalid pdf format) raised by PdfFileSecurity instance


I have a set of .pdf files that were created for me by a third party and I would like to concatenate a subset of those files into a single .pdf file (based on user input), then set the permissions to disallow editing the document. I'm using VB.NET.

I am able to concatenate the .pdf files (as MemoryStreams) in one MemoryStream. (And I'm able to write this resulting stream to Response.OutputStream and it works as expected.) However, when I initialize a new PdfFileSecurity instance with that resulting MemoryStream and try to execute any method (eg. ChangePassword() or SetPriviledge()), I get the following IOException:

Invalid pdf format:pdf head signature is not found!

Could the individual .pdf files be missing some necessary information? Or is some header information lost in the concatenation that I need to add back to the file?

Thanks in advance for your help.


Dear sthomas,

Thanks for considering Aspose.

Please reset the position at the begining of the result stream concatenated by many pdfs after concatenated like the following:

pdfStream.Position = 0

Any more question is welcome.

Best regards.