I've recently come across the DJVU file format before and needed to convert it to a PDF. The most reliable way I've found to do it is via the following command.
```bash
djvups FILENAME | ps2pdf - OUTPUT_FILE
```
Where FILENAME first gets converted to the PS file format which then gets converted to a PDF with the name OUTPUT_FILE. To make things easier, I wrote a little script that does this process automatically while preserving the filename.