Play Books lets you upload your own ePub and PDF, annotations, etc. They don't have PC app but you can use web browser. Mostly the issue is there is no concept of folders or tags and sort order is always by Recent, to organize content so you have to depend on Search as your library scales up. But it is free, and has a great annotation export feature.
Bookari and Bluefire Reader are a couple of other options. Both support Adobe DRM, and have apps for iOS and Android (BF has a PC app, Bookari has a browser reader). Of those two I think Bookari is more feature rich and focused on end users. But I have never used sync features of either.
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