When working with several larger images into a Proton document you can quickly run into the file size limit of 25MB.
Going back and deleting said pictures is also of no help, as they are still kept in the document history, and now any further changes of that file are held ******* by said history. Not even rollbacks to previous versions are possible.

There are currently two ways around this.
1: Create a copy of the document (and re-share any links, in case of a shared document)
2: Disable all file history for everything in Proton Drive.

Option 1 is a hassle and breaks up your workflow, option 2 opens any file open to the possibility of data loss.

Therefore file history should not count towards the document file size limit.
Or; file history should be able to be deleted/disabled on a file-by-file basis.