Depends ok the DRM technology. The only PDF DRM I came across so far was using the horrible feature by adobe digital editions.

It can be removed by using calibre and an unofficial plugin called noDRM, which should work on Mac as well (didnt test it tho, I dont own a Mac. Worked fine on windows tho)

Dream Theater and Classical music have entered the chat

Was actually confronted with the same problem - thank you for the solution!

Aegis authenticator. Beats all proprietary apps I’ve tried so far

Depends ok the cloud solution you use, but it definitely could be an issue. Probably not because of locking, but because the files probably aren’t locked with the clientson there could be issues while merging the changes.

It seems to be file based, so wouldn’t it be able to use other self-hosted sync-tools like the next cloud client (given you’re hosting your own instance)?