usually these extensions cover more than 1 type of files
so i try just comment most used
AX - DXshow filter libraries
ACM - driver for Audio Compression Manager
BPL - library for Delphi, used by Borland compiler etc.
CNV - DB2 conversion libraries
DRV - Device drivers and so on
FON - type of font file, allows possible code execution ...
QTX, Q3X, QTS - quicktime main libraries
PYD - Dynamic Python extension module in dll format
RLL - Microsoft SQLserver resource library
RPV - Real Player libraries for visual plugins
TLB - Borland library, OLE library etc.
WPC - Microsoft Word/WordPerfect file converter and/or mapping library
X32 - program extensions of macromedia software
XLL - Microsoft Excel Addin library
XRS - another RealPlayer plugin now for external resources
etc
...
i'm really lazy to find all the description but all of them got possibility to get infected&executed ...