Tidzy finds files on your Mac by what's in them. It reads the text in screenshots, photos and PDFs, so "wifi password" finds the screenshot, and you can copy the text right out. It also clears junk safely and spots passwords left lying around. All on-device.
Copse remembers everything you copy. Press ⌘⇧V in any app to search and paste text, links, code, images and files, even by the words inside screenshots. Paste Stack fills forms in seconds. Private and on your Mac. Free for 7 days, then $2.99 once.