The iPhone version of Google Drive has less flexibility. After opening a PDF, you'll see a Fill out form option at the bottom indicating whether Google Drive can fill out the form.
Google Drive is another free option ... with Adobe Scan acting as a nice middle ground that works with both. The iPhone ...
To avoid that issue, you can use iCloud Drive on your iPhone to store your documents. You just have to know how to set it up and access it. What is iCloud Drive? iCloud Drive is basically ...