Semi-related tip: I despise protected pdfs with a passion. Especially when you download a datasheet and you can't add annotations or highlights to it. So, how to remove this protection? One way is to print to postscript and convert back to pdf, but then you can't copy text from it. Here's how (on windows): download qpdf ( http://qpdf.sourceforge.net/ ) and run qpdf.exe -decrypt encrypted.pdf woho.pdf I made a small b…
It's funny how this isn't even about encrypted pdfs but plain ones.
Since this is a common 'technique' to 'protect' PDF documents, as some PDF viewers (such as Adobe reader) won't allow selecting text on these 'protected' PDF's. It's so common that most PDF tools assume an empty string if no password is explicitly supplied.
Source: I run a SaaS that converts PDF invoices to structured data, so I've examined quite a few PDF files the last couple of years.