CamScanner is a great app that I use quite often. The app is available for iOS and Android and the free version is very useful. The paid version, $4.99 on both platforms, adds some useful features, like uploading directly to Evernote. You get a 7 day trial of the paid version free, and can get an additional 60 day trial by sharing it on social networks.
The app allows you to take a picture of a paper document, crop/clear background/improve quality, and then save it as a PDF file. Take a picture of important documents, meeting agendas, whiteboards, and more and save them as PDF files for future reference and use. You can add tags to the files too, and search text in the scanned picture. You can then share the file to cloud services like Dropbox, Google Docs, Evernote, and more.
This app turns your smartphone into a scanner and document processor. Give it a try.
Google Play Store
Apple App Store