I saw some reviews posted that kind of bashed the app. I to was in this mode and looking for a better app. However the start guide that came with the app was of little help. By going to the support page on line I was able to find a manual and so far all my issues have been resolved. My suggestion at this time would be a link under settings to access your site to the manual which is well laid out and easy to follow and offers step by step help. In addition how about making the manual available as a PDF to be added to the document section of the app (please keep the hyper links live). Oh and yes beyond the undo button there is not a eraser, but there is an even better way to correct or delete markings even after closing and reopening the app. Seek out the online manual and you will see. And the manual to the app download and get a 5 star rating.
David Alan 99 about PDFpen 5 – PDF Editor, v2.5