This semester in university I had one professor that distributed lectures and other learning material as PDF files. Sounds perfect! I can use them and take notes directly on my iPad! – Me Nope, because these PDFs are not writable and protected by a password, rendering iPad note taking impossible. I mean, why would anyone lock a PDF file of a lecture in the first place? After a brief Google search, I learned that PDFs like mine can be unlocked by a high number of tools (qpdf, pdftk, …) wit...
