title_body: Conversion of djvu file into pdf file without increasing file size
upvoted_answer: The short answer is: PDF is not a good format for storing image data. The only reason that it is often used for doing so, is that it is one of the few formats (the other more well known ones are DjVu and TIFF), that allow you to store multiple (scanned) images in a single file. 
  
  The longer answer is that the possible storage of image data in PDF files is done in a less efficient way than is possible in the way DjVu does. So in general, unless the DjVu file is compressed inefficiently to start with, you will always get a bigger PDF file, or you get a much worse quality image. 
  
  The primary difference, apart from algorithms used for compression, is that an image in a DjVu file consists of multiple layers, each compressed separately, with optimized algorithms for the layer's data (monotone, color etc.), and recombined for display/printing. Especially on a page with characters (not selectable text associated with the characters) combined with images DjVu easily gets 20x smaller files at similar lossy quality.