I use an app called FastScanner and it does the same. It maintains a pdf for each aircraft I fly and after every flight I just add the latest page of the aircraft logbook to the specific pdf. It means I can always go back and check entries without going to the airfield, and it means I have a backup in case the logbook gets lost. The app also does folders so I have one for aircraft, another for students, a third for training flight notes and so on. It is free or advert-free and the only drawback (to me) is that is does not automatically sync with e.g. dropbox so back-up has to be done manually.
