You've probably encountered a PDF that doesn't allow printing or copying text to paste into a document. There are various restrictions, and there's a very easy way to bypass this,
silviolobo tested and approved PDF Pirate (org) http://pdfpirate.org/ it's very simple to use, you access the address on the website, and choose the option "Remove restrictions" then you indicate the file, wait until the end, and you will download the file, already without any restrictions.
For this service, access the site: http://pdfpirate.org/
PDFpirate
