Fix Acrobat Compare Documents Finding No Differences in Scanned PDFs
Question details
Users encounter an issue where the document comparison feature reports zero differences between scanned PDFs, even when visual differences exist.
- Product
- Adobe Acrobat
- Device & OS
- not provided
- Scenario
- Comparing two scanned PDF documents to identify changes, revisions, or discrepancies.
- Observed behavior
- The software states that no differences were found because it processes the pages as flat images rather than comparing the underlying readable text.
Before attempting to compare the files, try selecting a single word with your mouse cursor. If you cannot highlight individual words, the document is an image-based PDF and requires text recognition (OCR) first.
Run OCR (Optical Character Recognition) on Both PDFs
Convert the flat page images into searchable text so the comparison tool can read and process the actual words.
Scanners capture documents as photographs of the page. Even though it looks like text to the human eye, the PDF software only sees a flat image.
To compare the underlying words, you must first run an OCR process to extract the text from the images.
Launch Adobe Acrobat and open the first scanned PDF document you want to compare.
Navigate to the 'Tools' tab at the top of the screen and select 'Scan & OCR' (labeled 'Enhance Scans' in older versions).
Click on 'Recognize Text' in the toolbar and select 'In This File'. Click the 'Recognize Text' button to convert the images into readable text.
Save the file, repeat this exact process for the second scanned document, and then run the 'Compare Documents' tool again.
Use WPS PDF to Recognize Text and Compare Documents
WPS Office includes a robust PDF editor equipped with advanced OCR capabilities and document comparison tools, making it easy to extract text and spot differences in scanned files.
- 1. Launch WPS PDF: Open WPS Office and launch the WPS PDF tool to view your scanned documents.
- 2. Extract text with OCR: Open your scanned PDF and click the 'OCR' button under the 'Tools' tab to convert the images into searchable text.
- 3. Open the Compare tool: Once both documents are searchable and saved, navigate to the 'Tools' tab and select 'Compare'.
- 4. Review differences: Select the original and modified files to generate a detailed, side-by-side comparison report highlighting all text changes.
Frequently Asked Questions
Why does my scanned PDF look like text but acts like an image?
Scanners capture physical documents as photographs (images) of the page. Without Optical Character Recognition (OCR), the PDF reader cannot identify the visual shapes as actual, editable text characters.
I ran OCR, but the comparison tool still finds no differences. What's wrong?
The OCR process might have failed or produced poor results due to low image quality, handwriting, or incorrect language settings. Check the scan resolution (aim for at least 300 DPI) and ensure the OCR language matches the document's text.
Can I compare a scanned PDF with a natively digital PDF?
Yes, but you must first run OCR on the scanned PDF to convert its images into searchable text. Once both documents contain readable text, the comparison tool will be able to process and highlight the differences accurately.
How do I know if my PDF already has searchable text?
Select the text tool or simply use your cursor in your PDF reader and try to highlight a specific word or paragraph. If the entire page highlights blue at once, or you cannot select individual words, the document is an image and requires OCR.
