xlsgen 4.0 makes it possible to encrypt PDF files so that a user has to enter a password in order to open said PDF file.

Very simple, it is actually the same exposure in the object model than the encryption for XLS and XLSX files. In order to do so, the EncryptionPassword property at the workbook level can be used.

Internal PDF buffers are encrypted and the user of an PDF display application has to enter a password in order to view the file.