I know I'm on the other side of the TB street, but feel my question will be better answered here. (edit - we have an android tablet)
My wife is learning to play harp. She's been using pdfs and jpegs she printed out from her teacher, but wants to start using an app. Does anyone know of a simple app she'd be able to load her music into, and add notes to herself (highlight, annotate, etc.) on the music? I searched a bit but I'm overwhelmed as most apps are more like music books... I'm lost. And I'd appreciate anyone's help. Thanks.
MobileSheets. Super Happy and Satisfied user. Android as well as Windows version. I have not used paper since 2021 at all.
I can find any tune out of 8,000 in a second using MobileSheets Pro, but I use the Set Lists feature for my Church gig and just keep advancing. Over the course of a year it's a huge number of songs, different ones each week. I can notate, annotate, and write on my tablet to my heart's content because of Samsung's stylus is just like I was writing with a pen or pencil on paper. It is so much easier to read, and I use color to help. I use blue for navigation notes. It has a stamp feature which includes all notes and symbols too. And if a 4 pages song, I can show page 1,2,3,1,2,4 or what ever order, and use a pedal. I use the left pedal to go to the last page where the ending is if need to end quickly. I even put my practice, lessons, and woodshedding on the tablet too. You can have multiple setlists, one is for my lessons, also can sort by genre, collections, and even albums, and artists, plus more. I use "lesson" as a genre to keep track of learning, and my teachers name also to further filter if need be.
It only took one session with my tablet to realize there is no going back to paper. Getting ready each week now that I'm setup takes a minute, no filing, putting in a binder, and returning it to the big music file box. AND no miss filings either. No fixing the holes with tape because they get torn over time. My office has been paperless for years, long before Covid. I feel like an idiot I didn't do the same with my music sooner.
I have all my fakebooks scan'd in and now you can get most as pdfs. You can print a single pdf page and import or you can import the whole fakebook and use the index files to sort the songs themselves. They are available at the MobileSheets website.
Most lesson books come as pdfs, and phone can do great things at converting to pdf in a pinch.
Between lesson books and fakebooks, you can easily reach that 8,000 song total which is the bulk. My church music is about 400 songs added as we do them, and the same about 400 for music used in jams amongst friends. Maybe another 100 or so personal lesson stuff added as I go.
Getting up and running with my immediate need was quick, it took longer to load everything, and the ongoing stuff was loaded as we got to that song. You can print pages from pdf to pdf to get running quickly. You can even do multi versions for the same song with different arrangements for different bands or settings.
This software has benefited from years of professional input based on real world needs.
I’m not using that every time, as most of my gigs only require single page sheets with chord charts and the occasional obbligato, but when things get more complicated the pedal is super useful. I own a cheapish Donner pedal I bought on Amazon a couple of years ago, works ok, charges on USB-C. Don’t know if that is available outside of Europe, though. 
