How to Convert a Scanned PDF to Kindle (OCR)

Many study notes and older books are only available as scanned photocopies. While they look fine on a computer, they're a nightmare for Kindle: they're not text, just images of pages. No converter can make the font bigger on a photo; you need to turn the image into text first.

How to check if your PDF is a scan

Open the PDF on your computer and try selecting a word with your mouse. If only the word highlights, your PDF contains real text. If the whole page highlights as a block, or nothing highlights, it’s just an image: a scan. Another clue: if you use Ctrl+F to search for a word that’s clearly visible but it doesn’t show up, it’s most likely a scan.

What is OCR?

OCR (Optical Character Recognition) is the process of reading letters from an image and turning them into text—just like a person reading a page. The most widely used open-source OCR engine is Tesseract, which reads Spanish with high accuracy if the scan is decent.

OCR alone only gives you raw text. After that, you still need to rebuild paragraphs, identify titles and the table of contents, and keep images in place—just like with any PDF conversion.

What can go wrong?

• Misread words: A smudge or blurry letter can turn “electrón” into “lectrón.” That’s why, after OCR, it’s smart to review any unknown words in context before fixing obvious mistakes.
• Formulas: OCR can’t interpret mathematical formulas; it just turns them into random letters. The right way is to detect them and keep them as images.
• Charts and photos: Same thing—these should be cropped and kept as images.
• Crooked or shadowed pages: These lower OCR accuracy. If you can, scan with straight pages and good lighting.

How Legible does it

When you upload a PDF to Legible, it checks each page to see if it’s text or an image. Scanned pages go through OCR in Spanish, English or Portuguese; charts and formulas are kept as sharp images; and words not found in the dictionary are checked in their sentence before correcting obvious errors. This also works with mixed PDFs, where some pages are scanned and others have text.

Before downloading, you can preview the finished Kindle book on a drawn Kindle screen, page by page. If a scanned formula looks off, you’ll see it there.

If you prefer a manual approach

Some programs add a text layer to scanned PDFs (for example, the “Recognize text” feature in some PDF readers). Once your PDF has selectable text, you can convert it like any other, following our guide on Send to Kindle with PDF. Keep in mind that this text layer keeps the original line breaks, so you’ll still need a converter to rebuild paragraphs for proper Kindle formatting.