Short answer
Optical character recognition (OCR) reads text from page images. Choose the language that matches the scan, run it locally, search for several known terms and compare names, numbers, tables and citations with the page image.
When to use this method
OCR adds a draft searchable text layer to an image-based PDF. Verify the text, reading order and accessibility against the page image, especially on poor scans and complex layouts.
How we checked this guideSee what we reviewed, what we confirmed, and where the feature stops.
- What we reviewed
- Reviewed local OCR and its 16 optional Tesseract language data packs, whose SHA-256 checksums (digital fingerprints) are verified before use.
- What we confirmed
- The selected language model is downloaded on request and OCR runs locally after installation.
- Important limit
- Skew, handwriting, low resolution, unusual fonts, mixed languages and complex columns can produce incorrect or missing text.
What you need before running OCR
OCR means optical character recognition: software looks at page pixels and guesses the characters they show. Osenpa PDF Tools accepts supported PDF, JPG, PNG, BMP, TIFF and WebP input. Choose one installed language or all installed languages, then create a searchable PDF, UTF-8 TXT file or in-app preview. Searchable PDF is the starting output choice.
Create and verify a searchable copy
Inspect the scan
Check resolution, rotation and contrast before OCR.
Install the matching language
Choose the verified language pack that best matches the document.
Run OCR to a new file
Keep the original scan and create a separate searchable result.
Test the text layer
Search known names and phrases, copy a sample and compare critical facts with the page image.
Checkpoint: test recognition against the page image
Search for several known words on different pages, then copy a short passage and compare it with the scan. Check names, numbers, tables and citations character by character when accuracy matters. A searchable result can still contain OCR errors, so keep the original page image as the source of truth.
If search misses words or copied text is wrong
Check that the page is upright, readable and matched to the selected language data. Try the relevant installed languages when a document mixes languages. Skew, handwriting, low resolution, unusual fonts, tables and columns can still confuse OCR. Correct important names and numbers in your downstream work; do not treat recognized text as a certified transcription.
OCR assumptions
- Treating recognized text as an exact transcription
- Using the wrong language model
- Skipping tables, equations, names and page-number checks
Searchable PDF checks
- Known phrases can be found.
- Critical names and numbers match the image.
- The page image remains readable and aligned.
Osenpa PDF Tools
Run OCR locally with optional verified language data, then create searchable PDF, UTF-8 text or preview output that you can check.