Take a look at this one for working with PDFs for example: https://github.com/anthropics/skills/blob/main/document-skil... - it includes a quickstart guide to using the Python pypdf module, then expands on that with some useful scripts for common patterns.

The problem skills solve is initial mapping of available information. A tool might hide what information it contains until used, this approach puts a table of contents for docs in the context, so the model is aware and can navigate to desired information as needed.