How to exclude files from installing in the final package

All, I'm doing a lot of cleanup work with the help handbook files. kdiff3 contains many html files that get included in the final package. Originally the html files were intended for users not using KDE3. These html files cause problems with the help handbook table of contents and cause error messages seen in the xsession- error log. I want to modify the Makefile.am file not to include the html files in the package. I've looked around the web in frustration. How do I do that? Thanks? Darrell