The real life Command/Ctrl + F
Ftwfy is a open source Android App that uses the Mobile Vision API to allow you to search for any occurrence of a text in a digital document, for example: printed papers, books or non-handwriten texts. To make things even better, you can make use of regexes to optimize your search.
It was developed in Kotlin using Google's Android Open Source code, and it has open issues, so everybody is invited to contribute.