To register the COM object please run the following.
Where $INSTDIR is the COM file installation path. Once this is done please check the domcnfg once again.
If you cannot see the DominoPDF COM object after registering in the DCOMCNFG screen you may need to check the 32-bit DCOM config manager.
To configure 32-bit DCOM applications enter the following in a command line;
C:\WINDOWS\SysWOW64\mmc comexp.msc /32
Follow the interface security settings instructions as per the KB article.
Note: Be sure to run all /regserver and command line actions as an Administrator.