Conversion always comes along with quality-losses, unless you are willing to put up with larger output files than the original document. Since DjVu documents perform pretty similar to PDFs and even are searchable in many cases (which is often forgotten) it might be a good choice to stick with the original document choosing an adequate viewer. There is a whole bunch of DjVu Viewers for nearly all operating systems available in the web, a small selection of which is presented here in brief:
DjView is a handsome DjVu reader which is available for free for the operating systems Windows, Linux and Mac.
It allows to search DjVu documents and can display outline of the document and thumbnails of the the particular pages.
Windows Macintosh Linux
Another useful tool which is offering about the same functionality as DjView. In addition it allows to highlight and copy text with the cursor what makes you feel like dealing with a PDF document. Also the user interface is pretty similar to most PDF readers. As the names already imply the software is available for Windows and MacOs.
Windows & Macintosh
The STDU Viewer is a free (for non-commercial and educational use) and powerful document viewer which also supports DjVu. The software is available in different languages. It deals well with files which are equipped with a textlayer and therefore is useful if you want to export plain text from DjVu and other supported documents.
X Djvu for iPhone and iPad (2.99 $)
Yes, you can read DjVu documents with your iPhone! X Djvu is an useful application which enables you to read DjVu documents with an iPhone or iPad offering a lot of different features. The reduced X Djvu Lite version can be downloaded for free for testing.
Ebookdroid - a Document Reader for Android
You want to read your DjVu documents also on your Smart Phone using Android. No problem! There are also many free document readers available which allow to open DjVus on Android. A good one for example is Ebookdroid which also supports PDF. The installation is very easy via the Google App Store.