Hi Jcreighton,
Sorry to hear about the trouble.
Looking at the information shared above, it seems that there is some trouble using drawing and highlighting tool in Acrobat Reader mobile app?
Could you share more information on what exactly happen when you are trying to highlight? Is there any error message comes up?
Are you running the latest version of Adobe Acrobat Reader app? If not, you may check if there is any pending update in "PlayStore"
Also, it might be a file specific issue so you may check with a different file.
You can go through the related help article here- Unable to highlight text in a PDF.
Regards,
Akanchha