DjVu is a computer file format designed primarily to store scanned documents, especially those containing a combination of text, line drawings, indexed color images, and photographs. [...] DjVu has been promoted as an alternative to PDF, promising smaller files than PDF for most scanned documents.
aloisdg
commented
8 years ago
source Wikipedia
We support PDF, why not an open source alternative?
more info about DjVu on their official website.