OCR Explained: Turning Scanned PDFs Into Searchable Text
The difference between a scanned PDF and a text PDF, what OCR can realistically achieve, and why the output always needs checking.
Two PDFs can look identical on screen and be completely different inside. One contains text; the other contains a photograph of text. Almost every frustration with scanned documents traces back to this distinction.
How to tell which you have
Open the file and try to select a word. If a text cursor appears and you can highlight individual words, the PDF has a text layer. If your selection draws a rectangle over the whole area instead, the page is an image and there is no text to select.
A scanned PDF cannot be searched, cannot be copied from, and cannot be read aloud by a screen reader — because as far as the file is concerned, there are no words on the page, only pixels.
What OCR does
Optical character recognition analyses the image, finds shapes that look like characters, and works out which characters they are. Good OCR software then writes the recognised text back into the PDF as an invisible layer positioned exactly over the corresponding pixels.
That last detail is what makes the result useful. The page still looks exactly like the original scan, but selecting, searching and copying now work, because there is real text sitting behind the image.
What affects accuracy
- Resolution. Around 300 dpi is the usual sweet spot. Much lower and characters blur together; much higher rarely helps and slows processing.
- Contrast and skew. Clean black-on-white scans that sit straight recognise far better than grey, tilted photographs of pages.
- Language settings. Telling the engine which language to expect substantially improves accuracy, because it can use a dictionary to resolve ambiguous shapes.
- Typeface. Standard serif and sans-serif text recognises well. Decorative fonts, dot-matrix print and heavy ligatures do not.
- Handwriting. Ordinary OCR is built for printed text. Handwriting needs a different class of model and remains unreliable for anything cursive.
Availability on Formynex
OCR is not currently available on Formynex. It depends on a recognition engine that runs on a server, and the tool page says so rather than implying otherwise.
In the meantime, PDF to JPG will give you the page images from a scan, which is useful if you need to feed them into another application. If your PDF does already contain text, PDF to Word will extract it directly.