Once again, there's a need to read an old raster format to extract data. This time it's DjVu which has been up for discussion before: https://knowledge.safe.com/questions/83571/djvu-file-format.html
The solution now is to use ImageMagick (see this idea: https://knowledge.safe.com/content/idea/97094/incorporate-imagemagick-in-to-fme.html)
But I suggest that FME should read DjVu native.