Of course, viewing is one thing; editing is another process. If you want to write something in an existing PDF file, and then save your changes, you have software such as, PDF Architect, iSkysoft ...

To write on a PDF on Android, open the PDF file in the Adobe Acrobat Reader: Edit PDF app, and tap on the Text icon. Select where you want to input new text and type away.

If you are wondering how to annotate a PDF on Windows, you can use free online tools and software that we have included in this article.