Viewers are programs, usually free, that allow you to see a file or document. An example you have probably used is Adobe Reader for viewing PDF files.
The ones we are concerned with here are for viewing drawing files.
Dwfviewer - From Autodesk is of limited usefulnes because it only allows you to view one type of file. To use it to view other types, you have to purchase a $200 + conversion prgram.
Brava Viewer - also called dwqviewer.exe is more flexible and allows you to view several formats.