When you need a document that looks the same everywhere, no matter which app opens the file, you need a PDF. They’re the closest thing we have to digital paper. PDF files are ubiquitous for detailed forms, eBooks, whitepapers, and anything else where you don’t want text and fields to move around depending on your device and window size.

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And they’re easy to use. Android today, you can view PDF files with built-in tools. You can often highlight text, fill out forms, and even add basic annotations—but want to edit the text or replace an image in a PDF? That’s where things get tricky.

We’ve tested fifteen PDF editors to find the best apps to both view and edit PDFs. Here are the apps to use the next time you need to tweak a PDF—along with tips to turn anything into a PDF.