With documentation it will only be used if it is visible. If they have to exit your program and go to a website and search it won't be used. If you have a prominent (not hidden in a menu) search for help option it will be used. Assuming the search function works well.
The documentation is HTML, but it's linked directly in the app, so you can get relevant information and tutorials about the function you're using.
Most of the time these inquiries are related to "can it do X", rather than "how do I do X" - my best guess is that they want something in writing (therefore passing the responsibility for making the claim to us), rather than doing their own reading and confirmation. It still takes a fair bit of effort to answer all of these.
