Can not save PDF file with inputs, error message "Document is encrypted"

I have inserted inputs to a form given as a PDF file. Using Evince document viewer 3.2.1 on Ubuntu 11.10, there is no problem with inserting inputs to the form and to print the result.

But it is not possible to save the PDF file with inputs (as a new file) and the following error message is given:

The file could not be saved as "file:///home/username/Downloads/file.pdf"

Document is encrypted

Note for the message above that if I try to save the file in a different folder (e.g. Documents), the error message is still referring to the Downloads folder.

How to save the PDF file with inputs?

P.S. I know that similar questions are in the database, but I have not seen a similar error message in previous questions

There is a bug report for Envince. Have a look for further information and status update, the bug is still open.

There is a possible workaround that seems to work for some users, you might try and let us know.

Run these steps on a terminal:

• Install the tool
  
  sudo apt-get update && sudo apt-get install qpdf

• Run this command, input.pdf is the source file and the output.pdf is the saved file after running the tool.
  
  qpdf --decrypt input.pdf output.pdf

Try opening the output.pdffile and doing your changes there.