Hello Darrenb,
We're sorry for the trouble you had, The Edit PDF feature is only available on iPad to subscribers to Acrobat Pro DC. iPad users have access to the new Edit Text feature which provides some of the same features found in the desktop version of Acrobat. This feature allows you to:
For detailed steps, refer to the help article Acrobat Reader Help for iOS: Edit a PDF
However, It's not possible to edit text or add text markup annotations (Highlight, Underline, Strikeout) to scanned PDF documents if it's not containing any text.
You need to turn scanned PDF documents into PDF documents with editable text using an OCR (Optical Character Recognition) tool. Acrobat Pro DC (desktop app) has a built-in OCR feature.
Because you have the Adobe Adobe Pro DC paid subscription service, you should be able to activate and register Acrobat Pro DC desktop app on your Windows/Mac computer.
Unfortunately, the OCR feature is not available in the Acrobat Reader mobile apps (for iOS, Android, Windows Phone).
Are you facing this issue with one specific PDF file or with all the PDF file?
If it is specific to one PDF file, is it possible to share the file with us so that we can test it at our end? To share the file, refer to How Do I Send Private Message
Let us know how it goes and share your observation.
Thanks,
Anand Sri.