The optional [MarginDiff PDF & OCR Add-on](https://margindiff.app/ocr/) provides PDF text recognition for MarginDiff
Documents. Check [Downloads](https://margindiff.app/downloads/#diffyocr) for installer availability;
public installers are not available. Ask Polywick Studio about OCR beta access.
PDF comparison in MarginDiff Documents requires the separately licensed Tungsten
Automation OCR worker to be installed and configured by an administrator.
See the [Glossary](/docs/glossary) for the OCR term.
## Prepare and compare
1. Confirm with your administrator that the OCR component is available.
2. Enable OCR in **Tools → Admin Options**, where available in your build.
3. Select the two input files in the comparison dialog.
4. Select **OCR**, then **Start**.
5. Review the result against the original PDF pages.
A PDF selected without the required OCR workflow is rejected rather than treated
as an empty document. If OCR is unavailable, convert the PDF to DOCX or RTF using
an appropriate tool, then compare the converted versions.
While OCR is converting the PDFs, comparison controls are temporarily unavailable.
Choose **Stop** to cancel the conversion. Cancelling removes the incomplete OCR
output and keeps any previous comparison open. Wait for conversion to finish or
cancel it before closing the window.
If the OCR worker crashes, fails, or produces no text output file, the comparison
does not proceed. Each PDF conversion has a five-minute timeout. Check the error
message and your OCR setup before retrying.
## Recognize OCR errors
Low-resolution scans, skewed pages, handwriting and complex layouts can produce
incorrect words or reading order. For example, a letter `O` may be recognized as
the digit `0`. That can appear as a difference even when the printed text did not
change.
Check names, numbers, tables and critical wording against the PDF itself. Use
the clearest available source and comparable conversion settings for both versions.
For protected PDFs, see [Protected inputs](/docs/privacy/#protected-inputs).
For other conversion problems, see [Troubleshooting](/docs/troubleshooting).