If I hit a single tab once the file opens that places me in the first fillable filed, Name in this case, and each successive tab takes me to the next fillable field, whether that's a text/edit box, check box, etc. My guess is that once one has focus on the fillable fields that is where it stays unless one uses the F5 command to shift focus back to the PDF document text, that's worth a try, anyway. Here is the latest collection of Adobe Reader DC keyboard shortcuts. In a particularly perversely funny twist the keyboard shortcuts for accessibility are available on this page but the direct link to them is hidden unless you hit "show more." Of course, a search on accessibility will get you there, too. That being said, the regular keyboard shortcuts may be far more pertinent.