Assigning PDFs in Google Classroom? If you can avoid them - I would - but sometimes it's what's needed. If so, using Read&Write PDF reader is one way to have students fill it out. Getting started takes a few steps, so I put together a video:

And here's how that same assignment would work for a student using an iOS device:

And since I didn't model how to turn in the PDF in my first video, here's an article with a bit more info - there's a checkbox in the PDF reader settings that will really help!: https://support.texthelp.com/help/how-to-use-the-texthelp-google-pdf-reader-with-google-classroom#Enable%20Classroom%20Integration

Aaaand since it was bugging me so much that I forgot to include that, I created an updated video with the whole student experience from start to finish: