A few days ago, whilst delivering one of our Start-up Essentials sessions on doing market research, I briefly mention that Google is your best friend for doing research, specially if you familiarise yourself with its advanced search operators.
Google itself has a great little basic guide on how to use them here: https://support.google.com/websearch/answer/2466433?hl=en
Though my absolute favourite is this one by the Australian SEO company Supple, because is more of a quick, simple, visual reference library: https://supple.com.au/tools/google-advanced-search-operators/
Regardless of which one you use, Google search operators are incredibly useful when searching for very specific information or documents in a certain format that normal general searches would otherwise not rank as relevant enough to show up in search results.
Don’t be scare to give them a try, you never know what hidden information gem you might find!