Originally Posted by charleski
DjVu doesn't contain text, it works on images, and that's your problem. It uses an image-compression technology that's highly optimised for text and allows far smaller file sizes than other formats that target more general image types.
contain a hidden text layer (which is used in the search feature). This layer can be extracted and used as the basis for any other conversion.
For example most of the DJVU files on The Internet Archive (TIA) contain such a layer and I have used them as a basis for FB2 books.
Of course the files the OP is working on may not have such a layer as the original text may not have been OCRd and associated with the image layer.