OCR for Scanned Documents
Scanned PDFs are essentially images — you can't select, copy, or edit the text. UnblockPDF's OCR (Optical Character Recognition) technology converts these images into searchable, editable text.
When to Use OCR
Use OCR when you have a scanned document, a photo of a page, or any PDF where the text is not selectable. Typical examples include scanned contracts from paper archives, photographed receipts and invoices, older documents that only exist as scans, and PDF files received via fax. A simple test: try to highlight text in the PDF with your mouse. If you cannot, it is an image-based PDF that needs OCR.
How OCR Works
Our OCR engine analyzes each page, identifies text characters in the images, and creates a text layer over the original scan. This means the visual appearance of your document stays the same, but an invisible text layer is added. This text layer allows you to search for words, copy text, and further process the content in other programs.
Step-by-Step Guide
1. Upload your PDF: Open your scanned document in the editor.
2. Start OCR recognition: The text recognition analyzes each page automatically. Depending on the number of pages and scan quality, this process takes a few seconds to a few minutes.
3. Review the result: Spot-check the recognized text, especially for numbers, proper names, and special characters.
4. Process further: Edit the recognized text in the editor or export the searchable PDF.
Tips for Better OCR Results
Recognition quality depends heavily on scan quality. Scan documents at a minimum of 300 DPI in grayscale or black and white. Make sure pages are aligned straight, as skewed scans lead to more recognition errors. If black borders or unnecessary areas are distracting, use the Crop tool before running OCR to process only the relevant page area. After text recognition, you can reduce the file size with the Compress tool, since the additional text layer barely changes the file size.
Further Processing After OCR
A searchable PDF is the first step. If you want to edit the content extensively, convert the document to Word format afterward. For pure archival purposes, converting to PDF/A is recommended, as it ensures long-term readability. Both workflows begin with a clean OCR result, making this step essential for any scanned document you plan to work with digitally.