Why Scanned PDFs Don't Work for Audio Conversion

If you've tried to convert a scanned PDF to an audiobook, you may have encountered an error message saying the file isn't supported. Here's why scanned PDFs don't work for audio conversion and what you can do about it.

The Difference Between Scanned and Text-Based PDFs

Text-Based PDFs

A text-based PDF contains actual text data. When you open the PDF and select text with your cursor, you can copy and paste it. This text is what gets converted to speech when creating an audiobook.

Scanned PDFs

A scanned PDF is essentially a collection of images. When you scan a paper document, the scanner creates pictures of each page. These images look like text, but to a computer, they're just pixels—no different from a photograph. There's no actual text data to extract.

Why This Matters for Audio Conversion

Text-to-speech technology works by:

1. Reading the text characters from the document
2. Analyzing pronunciation, sentence structure, and emphasis
3. Generating audio that speaks those words

With a scanned PDF, step 1 fails—there's no text to read. The file only contains images, and while you can see text in those images, the conversion software cannot.

How to Check If Your PDF Is Scanned

There's a simple test: open your PDF and try to select text by clicking and dragging your cursor.

• If you can select and copy text: Your PDF is text-based and will work for conversion.
• If you can't select text: Your PDF is likely scanned and won't work directly.

Solutions for Scanned PDFs

Option 1: Use OCR (Optical Character Recognition)

OCR software can analyze images and extract text from them. Common OCR tools include:

• Adobe Acrobat Pro (built-in OCR)
• Google Drive (upload and convert to Google Docs)
• ABBYY FineReader
• Free online OCR tools

After OCR processing, the text becomes selectable and the PDF can be converted to audio.

Option 2: Find a Text-Based Version

If the document is a published book or paper, a text-based version may already exist:

• Check the publisher's website for eBook versions
• Look for the document in academic databases
• Search for EPUB or other eBook formats

Option 3: Request an Accessible Copy

Many organizations are required to provide accessible versions of documents. If you have a disability, you may be able to request an accessible text version from the publisher or institution.

Why We Don't Support Scanned PDFs Directly

ListenablePDF focuses on providing high-quality audiobook conversions. OCR text extraction often introduces errors, especially with older scanned documents, poor scan quality, or unusual fonts. These errors would carry through to the audiobook, creating a poor listening experience.

By requiring text-based PDFs, we ensure the conversion is accurate and the final audiobook is high quality.

For more on what makes a good conversion, see best PDFs for audiobook conversion.