Looking at the app it says it uses PDF files, so anything that can turn your hard copy to PDFs.
For the best results, most flatbed copier/scanners should work. Some of them can be used directly with the iPad using their printer/scanner software. For instance, an HP all-in-one can be used to scan using the appropriate HP Printer app. You can also use your computer/laptop if you have one, then transfer the results to the iPad. There are several methods to do this, but probably the easiest is to use a cloud file service.
For pretty good results you can use a scanning app such as Scanner Pro by Readdle (the one I use), or ScanBot (good reviews). There are several other good ones. It takes a bit more care since you need good lighting and care to make the music lie flat for best results, but it’s cheap, easy, and adequate for most PDF scanning needs.
If find the scanner apps easier to use than a printer, and better than my supper cheap HP (which only has a feed type scanner). They are also easier to use with the iPhone than the iPad. At least for the scanning part. The editing and compiling software is of course easier on the larger screen. Most scanning apps will work on both the iPad and iPhone, and will sync between them.
