itextSharp - Merging pdf files disables extended reader permissions

Question

I\'m using Itextsharp v5.1 and created enabled reader pdf files. I wrote a c# class that fill the form and keep each individual pdf file extended reader. But, when I use this Me

Answer 1

Reader permissions can be enabled only by Adobe products. They are based on a custom digital signature that is invalidated when the file is modified. The certificate for this digital signature is owned by Adobe and it is not public, also the computation of this digital signature is not documented. You cannot re-enable in any way the reader permissions after you merged the files, unless you use Acrobat on the merged file.