"Performance. On Windows I really like to use Everything Search Engine. It provides instant results as you type for all your files and lots of useful features (regex, filters, bookmarks, ...). On Linux I couldn't find anything that's even remotely as fast and powerful."

https://www.lesbonscomptes.com/recoll/pages/index-recoll.htm...

"Recoll finds documents based on their contents as well as their file names."

"Recoll will index an MS-Word document stored as an attachment to an e-mail message inside a Thunderbird folder archived in a Zip file (and more… ). It will also help you search for it with a friendly and powerful interface, and let you open a copy of a PDF at the right page with two clicks. There is little that will remain hidden on your disk."