5 stars: This app has been great. Turns the photos of documents into scanned documents that look like they were scanned. I used to just take a regular photo and it was hard to get the right lighting, sizing, etc. Works great. I have the free version, which has adds, but they don't bother me like they can in some apps.
5 stars: I have struggled to find an app that can scan documents into PDF format that was user friendly. This app ended my search. It offers easy cropping, easy adding of pages and easy sharing. I am not sure how it will meet your needs for more complex tasks but if you are looking at free apps for complex tasks i think that will be your first problem. This is easy, clean, and simple.
4 stars: ** Update - the app is spontaneously working again as of August 29th. Hopefully no more issues. ** Great app, works well, I use it enough to justify paying for it. However, I cannot recommend it to to unreliability. My subscription vanished after a recent update, and has not been reinstated. The developer has not been able to fix it, and Google Play has refused to refund it. (Initial contact on July 4, no resolution yet as of August 22.)
4 stars: **FYI I'm a premium user. The app is pretty great. Easy to use, has a lot of useful features, and the scans are high quality. I do think the cost is too high considering there are valid free alternatives. Also, occasionally the devs change the UI of the app making the usage unintuitive, only to roll it back shortly aft...