What a searchable PDF is
A scanner or a phone scanning app saves each page as a picture. You can read it, but Ctrl+F finds nothing and you cannot select a single word. OCR (optical character recognition) finds the letters in those pictures and turns them into real text.
This tool puts the recognized text into the PDF as an invisible layer that sits exactly over the printed words. The pages look the same as before, because the scan itself is not touched or compressed again. But now you can search the document, select and copy sentences, and let document systems and search tools index it.
Mixed documents and languages
Choose the language the document is written in. If it mixes two, for example a German contract with English terms, add the second language and both are recognized together. Letters such as ç, ğ, ş, é, ñ and ß are kept in the searchable PDF and in the text file.
Pages that already contain real text, such as pages created on a computer or a PDF that was run through OCR before, are recognized automatically and left unchanged. Their text still goes into the TXT file.
Getting good results
Clear scans of printed text at 200 to 300 DPI give the best accuracy. Pages are rendered at about 300 DPI before reading, so small print is enlarged. Handwriting, very faint copies and text on busy backgrounds are hard to read for any OCR, so check names and numbers before you rely on them.