Which online subscription service did you purchase? "Export PDF" or "Acrobat Pro DC"?
The EditPDF feature is available only to "Acrobat Pro DC" subscribers.
In the Acrobat DC for iOS app, you can only view non-PDF documents (e.g. Word, Excel, PowerPoint). To edit a non-PDF document, you will need to open it in other mobile app such as Microsoft Word for iOS.
Please let us know if you have additional questions. Thank you.