What is OCR for PDF forms?
Definition
OCR (optical character recognition) reads the text in a scanned or image-based document and converts it from pixels into machine-readable characters. For a scanned PDF form, OCR recovers the labels and text that a plain image does not expose.
Why scanned forms need it
A scan is just an image of a page; the words on it are not text a computer can read. OCR recognizes those words, which makes it possible to understand the form's labels and locate where each input belongs.
Where it fits in making a form fillable
On a scanned form, OCR comes first: recover the text, then detect the fields using both that text and the page layout, then place interactive fields. Without OCR, a scanned form is opaque to field detection.