Unprotect a protected pdf
If you're not averse to using the terminal, there's a package called qpdf that you can install. It's in the software center. To remove protections from your file you can use something like this:
qpdf --password=your_password --decrypt yourfile.pdf output.pdf
That should do the job. As a side note, another useful (also command line) tool to have for working with pdf files is pdftk.
Example from man pdftk:
pdftk secured.pdf input_pw foopass output unsecured.pdf
Hope that helps!
On Ubuntu 18.04 neither of two commands worked! (I don't know why). I followed the instructions to install pdftk (since it's no included in the repositories). However I figured it out (I think) in a simple way...
evince mydocument.pdf- ctrl+p
- Print to File (choose a new file name (or overwriting))
That's it, I could to highlight with Foxit Reader.