How to password protect a PDF without Acrobat using free built-in tools on your computer. In this tutorial, I'll show you how to add a password to a PDF file on Windows PC, Laptop, iPhone, Android, Chromebook and Mac so you can secure sensitive documents without downloading any extra software. This means you can keep your PDFs private and protected in just a few clicks. To do this we use a tool I built called PDFGadget. PDFGadget allows you to password protect PDFs for free without installing so