DjVu

Pronounced like deja vu.

It is a graphics file format, like Jpeg, Gif, Tiff. 

It is a highly compressed yet high quality colour format.  Used primarily for archive storage of documents.  

You will need a special viewer .   One of these is  https://windjview.sourceforge.io/en/ 

We no longer convert these files to the convenient pdf file format.  The files are extremely large and we have had many customers report they are still unable to open the pdf.   We only provide access to djvu for these file types now.