Converting djvu to pdf AND preserving table of contents , how is it possible?

update: user3124688 has coded up this process in the script dpsprep.

I don't know of any tools that will do the conversion for you. You certainly should be able to do it, but it might take a little work. I'll outline the basic process. You'll need the open source command line utilities pdftk and djvused (part of DjVuLibre). These are available from your package manager (GNU/Linux) or their websites (Windows, OS X).

• step 1: convert the file text

  First, use any tool to convert the DJVU file to a PDF (without bookmarks).

  Suppose the files are called filename.djvu and filename.pdf.

• step 2: extract DJVU outline

  Next, output the DJVU outline data to a file, like this:

  djvused "filename.djvu" -e 'print-outline' > bmarks.out
  

  This is a file listing the DJVU documents bookmarks in a serialized tree format. In fact it's just a SEXPR, and can be easily parsed. The format is as follows:

  file ::= (bookmarks
             <bookmark>*)
  bookmark ::= (name
                 page
                 <bookmark>*)
  name ::= "<character>*"
  page ::= "#<digit>+"
  

  For example:

  (bookmarks
    ("bmark1"
      "#1")
    ("bmark2"
      "#5"
      ("bmark2subbmark1"
        "#6")
      ("bmark2subbmark2"
        "#7"))
    ("bmark3"
      "#9"
      ...))
  

• step 3: convert DJVU outline to PDF metadata format

  Now, we need to convert these bookmarks into the format required by PDF metadata. This file has format:

  file ::= <entry>*
  entry ::= BookmarkBegin
            BookmarkTitle: <title>
            BookmarkLevel: <number>
            BookmarkPageNumber: <number>
  title ::= <character>*
  

  So our example would become:

   BookmarkBegin
   BookmarkTitle: bmark1
   BookmarkLevel: 1
   BookmarkPageNumber: 1
   BookmarkBegin
   BookmarkTitle: bmark2
   BookmarkLevel: 1
   BookmarkPageNumber: 5
   BookmarkBegin
   BookmarkTitle: bmark2subbmark1
   BookmarkLevel: 2
   BookmarkPageNumber: 6
   BookmarkBegin
   BookmarkTitle: bmark2subbmark2
   BookmarkLevel: 2
   BookmarkPageNumber: 7
   BookmarkBegin
   BookmarkTitle: bmark3
   BookmarkLevel: 1
   BookmarkPageNumber: 9
  

  Basically, you just need to write a script to walk the SEXPR tree, keeping track of the level, and output the name, page number and level of each entry it comes to, in the correct format.

• step 4: extract PDF metadata and splice in converted bookmarks

  Once you've got the converted list, output the PDF metadata from your converted PDF file:

  pdftk "filename.pdf" dump_data > pdfmetadata.out
  

  Now, open the file and find the line that begins: NumberOfPages:

  insert the converted bookmarks after this line. Save the new file as pdfmetadata.in

• step 5: create PDF with bookmarks

  Now we can create a new PDF file incorporating this metadata:

  pdftk "filename.pdf" update_info "pdfmetadata.in" output out.pdf
  

  The file out.pdf should be a copy of your PDF with the bookmarks imported from the DJVU file.

Based on the very clear outline above given by user @pyrocrasty (thank you!), I have implemented a DJVU to PDF converter which preserves both OCR'd text and the bookmark structure. You may find it here:

https://github.com/kcroker/dpsprep

Acknowledgements for the OCR data go to @zetah on the Ubuntu forums!