Dynamic Link Library files (.dll files) are used so different programs in Windows can share the same functionality. Normally these would be systems files on one's de-NIST list - non-responsive electronic files to be removed for the data set for review. However it is possible to view the contents of .dll files and see which functions they specify.
NirSoft's DDL Export Viewer can be downloaded here. It will generate a list of functions in each .dll file. Just a little Window into the obscure world of system files.