What OCR is and how to make a PDF searchable
OCR (optical character recognition) is the technology that identifies the letters in the image of a page. Applied to a scanned PDF with the PDF to OCR tool, it adds an invisible text layer that lets you search, select and copy the content without changing how the pages look.
The problem with scanned PDFs
When you scan a sheet of paper, the scanner produces an image. The resulting PDF looks like a document, but inside it is a sequence of photos. That is why you cannot search for a word, copy a passage or select a paragraph: to the computer there is no text, only pixels.
What OCR is
OCR stands for optical character recognition. It is the technology that analyzes the image of a page, identifies the letters and produces the corresponding text. Applied to a scanned PDF, OCR adds an invisible text layer behind the image: the look of the page does not change, but the text can now be searched, selected and copied.
How to run OCR on a PDF
With the PDF to OCR tool:
- Upload the scanned PDF.
- Choose the document language. The tool recognizes English, Portuguese, Spanish, French, German and Italian.
- Click process and wait. Long documents may take a few minutes.
- Download the PDF and test it: use your reader’s search to look for a word from the document.
If you only have photos, not a PDF
If the documents are images (JPG, PNG, HEIC), use OCR to PDF, which combines the images into a single PDF, one page per image, with the text already recognized. And if you have not scanned the document yet, PDF Scanner uses your phone or computer camera to photograph the pages and create the PDF, with an OCR option.
How to get good recognition
OCR quality depends mainly on image quality:
- Scan at 200 to 300 dpi. Lower resolutions lose letter detail; higher ones only make the file bigger.
- Keep the page straight and well lit, without shadows or folds.
- Choose the correct language: a text recognized in the wrong language loses accents and special characters.
- Prefer sharp originals. Handwriting, stamps over the text and blurry photos give worse results.
What to do with the recognized text
With a searchable PDF, you can find information in seconds and copy passages into other documents. If you want to edit the content, run PDF to Word after OCR. No OCR is flawless, so review numbers, names and dates before using the text for anything important.
Frequently asked questions
How do I know if my PDF needs OCR?
Try to select a sentence with the mouse. If the cursor selects the whole page as an image, or search does not find visible words, the PDF is scanned and needs OCR.
Which languages does the OCR recognize?
English, Portuguese, Spanish, French, German and Italian. Choosing the right language improves recognition of accents and special characters.
Does OCR work with handwriting?
Results with handwriting are limited. OCR works best with printed text scanned at 200–300 dpi, with the page straight and well lit.