There was Text Fairy which was FOSS until version 4.0.0 but unfortunately was made closed source with ads and it is now only available from play store (current version 5.3.2). The closed source version is actually quite good but the ads are very annoying.

I recently found another FOSS app for scanning documents. The OSS Document Scanner can be used to scan documents by making a photo or importing an image file. It has OCR and can export as PDF. It is MIT licensed and can be downloaded from play store or via f-droid from IzzyOnDroid repo.