[anno_visser@hotmail.com]

Oh sorry, I misread your post (it was late). You can't merge annotations - it's just not supported, as there are too many things that can go wrong because there is no way to uniquely identify annotations to understand when annotations have been edited or removed. You can use multiple layers and have her annotations in one layer and your annotations in another layer, but that will only work if you only annotate on one device at a time before synchronizing changes. I may support an option in the future to choose which layers are synchronized (based on layer name, as it would be far too tedious to try to provide a selection UI where you could dig down into every page of every song to pick individual layers).

Mike

Thank you for the clarification about the annotations are not possible to merge. 
So what if i create two songs of the same pdf , let's say an A and a B version.
She makes annotations on the A version and I on the B version, after the choir we come home and start syncing. 
Is there a possiblity to make it work ?
How should i do the syncing then ? 

Maybe for background info....
It's still not clear to me what 2 way syncing does.
Since i am a new user, i don't have a lot of experience but from my little experience, the 2 way sync was working fine untill i started to use setlist and deleted/renamed some setlists then the 2 way sync didn't work as expected. if 2 way sync is working like google drive desktop then it should be fine. During choir practice while we sing i don't make new setists only annotations, i am thinking perhaps i can use the two sync then ?
(just thinking up loudly here)