Would you provide more information about the problem?
Acrobat Reader for iOS itself is a free app that provides basic functionality (viewing PDF documents, commenting, form filling, searching, printing, sharing files, etc.). But you will need an online subscription service to convert from/to PDF.
Which online subscription service did you purchase? Adobe Export PDF, Adobe PDF Pack or Adobe Acrobat Pro DC?
Do you see an error message? Would you provide a screenshot?