Hmm.. after running the deDRM python script manually, I get this as part of the conversion log:
Code:
Processing Section: metadata
.
Successfully Extracted Topaz contents
Updating to color images if available
Creating cover.jpg
Processing Dictionary
Processing Meta Data and creating OPF
Processing StyleSheet
Using font size: 116
Using page height: 12960
Using page width: 8640
Processing Glyphs
....
Processing Pages
....
Processing Complete
Book Successfully generated
Creating NoDRM HTMLZ Archive
Creating SVG HTMLZ Archive
Creating XML ZIP Archive
So this might've been a Topaz file?