OmniDocHow to perform OCR text recognition on PDF scans
Scanned PDFs cannot be copied or searched, and OCR needs to be performed first to generate a text layer. This article explains how to determine whether a file needs to be identified, use the PDF editor of the OmniDoc desktop client to complete the identification, and check the results item by item.
Key points of this article
- PDFs that can select text do not require OCR, only full-page images that cannot be selected need to be recognized.
- Try using one or two pages first to confirm the recognition effect before processing the entire page, which can save a lot of rework.
- After identification, numbers, dates, names and professional terms must be checked against the original image, and the OCR results require manual review.
- When editable format is required, it is easier to complete OCR first and then export to Word or Excel for modification.
- When the scanned document is blurry, skewed or has low contrast, rescan or rotate the page before recognition.
Scanned PDFs are usually obtained by taking photos or scanning paper documents. What you see on the page are text, but they are actually just pictures. Therefore, text cannot be copied, keywords cannot be searched, and modifications cannot be made directly. The function of OCR (optical character recognition) is to recognize the words in the picture and generate a text layer that can be selected, copied and edited.
This article is written for those who have scanned contracts, scanned papers, old materials or photographed PDFs and want to turn the content into usable text. The following will first help you determine whether the file requires OCR, then use the PDF editor of the OmniDoc desktop client to complete the recognition, and finally explain how to check the results.
How to perform OCR text recognition on scanned PDF? One sentence conclusion
If the text in the PDF cannot be selected, you need to do OCR first; check after the recognition is completed, and then export or continue to use it, which is safer than using the recognition results directly.
| your situation | Recommended practices | reason |
|---|---|---|
| Text can be selected and copied | No OCR required, edit or export directly | The file already has a text layer, and re-recognizing it may introduce errors. |
| The entire copy is a scanned copy or a photo-combined PDF | Do OCR with a desktop client PDF editor | Generate a text layer before you can search, edit or export it |
| Only translation is required, no need to retain the original text | Upload the scanned PDF to the web page for translation | The translation process supports scanned copies, and you can download only the translation by selecting it. |
| After identification, you need to change the format or make a form. | OCR first, then export to Word or Excel | After the text is converted to editable format, it is easier to adjust |
| Pages are blurry, have handwritten annotations or seals | Manually check the blurred pages first and rescan if necessary | The clarity of the original image directly affects the recognition results |
Before you start: Confirm these points first
- Confirm whether the file is a scanned copy. Open the PDF and try to select a piece of text with the mouse. If the image cannot be selected, or a full page image is selected, OCR is required. This step can avoid repeated recognition of files that already have text layers.
- Check the clarity of the original image. If the scanning resolution is low and the page is shaded or slanted, it is easy to make errors in the recognized words. It is recommended to re-scan important documents with clear originals and then identify them.
- Estimate number of pages and wait time. A 30-page paper can be processed in its entirety, but time should be reserved for longer pages. It is recommended to select a few pages to try out first, and then process all pages after confirming the effect.
- Clearly identified purpose. If you only search for keywords, the verification can be rough; if you want to quote figures or terms, you must verify them word for word, and compare them with the originals if necessary.
- Keep original files. Both OCR and editing will change the PDF. Make a backup copy of the scanned original, so you can go back and redo it if something goes wrong.
Steps to OCR scanned PDFs in OmniDoc desktop client
- Download and open the desktop client. Get the Windows, macOS or Linux version from download.omnidoc.top and open the PDF editor after installation.
- Import scanned PDF. Drag the file into the editor or load it by opening the file. After loading, take a look at whether the page is clear and oriented correctly.
- Check the page orientation. If there is a page that is horizontal or upside down, use the rotation function to adjust it first, and then do the recognition, otherwise the recognition sequence may be messed up.
- Try it on the sample page first. Select the first few pages or a typical page to run the recognition, observe whether the text corresponds to the original page, and determine whether the quality of the original image is acceptable.
- Run OCR recognition. Start the recognition in the OCR function of the editor, wait patiently when the number of pages is large, and do not close the software during the recognition process.
- Check and modify the recognition results. Open a few random pages and check numbers, dates, and terminology against the original images. If you find a typo, you can directly edit the paragraph text and save it after correction.
- Export or save according to usage. Export to Word or Excel when editable format is required; save the modified file only if you want to keep the PDF.
- Upload when translation is needed. If you want to translate the content into other languages, you can upload files to the translation portal corresponding to app.unidoc.top on the web page, select bilingual comparison or translation only, download the results, and check the terms and numbers in the translation.
Check each item after completion
| Check items | How to see | What to do if there is a problem |
|---|---|---|
| Can text be selected? | Select a piece of text and copy it to Notepad | If it still cannot be selected, it means that the recognition is not completed. Re-run and confirm the page range. |
| numbers and dates | Check the amount, date, and number item by item against the original picture. | Modify paragraph text directly in PDF, then check again after correction |
| Paragraphs and line breaks | Check whether the paragraphs are serial and whether the line breaks are abnormal. | Export to Word and then adjust, or just use the PDF for search |
| Tables and formulas | Check whether table columns are aligned and whether formulas are incomplete | It is recommended to manually proofread complex tables and formulas against the originals. |
| Complete pages | Compare the number of pages and check if there are any blank pages or missing pages | Re-import and confirm that the original file is not damaged |
| Originals retained | Confirm that the scanned original still exists | If there is any doubt about the result, go back to the original document and re-identify it. |
Both OCR and machine translation are subject to errors and omissions. Important content in contracts, papers, medical and legal texts must be checked against the originals.
❓ Frequently Asked Questions (FAQ)
1. What is the difference between OCR text recognition done online and using a desktop client?
Online conversion websites are suitable for small files that are occasionally processed. Please pay attention to file size restrictions and privacy terms before using them. The PDF editor on the desktop client can modify, compare and export directly after recognition, which is more suitable for files that need to be checked repeatedly.
2. How to convert image PDF into editable text?
First do OCR to generate a text layer, then export it to Word or Excel, and continue to modify it in desktop office software. You only need to correct a few typos and modify the paragraph text directly in the PDF editor.
3. How to convert image PDF to text PDF?
After the recognition is completed, the text in the PDF can be selected and searched. This can be confirmed by selecting a piece of text. The original scan is just an image, and the text layer is only available after recognition.
4. After scanning and translating online recognition, can the results be used directly?
Translation results require checking of terms, names and numbers, especially for contracts, medical and legal texts. On the web page, you can choose bilingual comparison, putting the original text and the translation together to facilitate paragraph-by-paragraph comparison.
5. What should I do if the characters cannot be recognized on the scanned document?
In most cases, the original image is blurry, tilted or has low contrast. It is recommended to redo it with a clearer scan and rotate the skewed page first before identifying it.
📝 Summary
When performing OCR text recognition on scanned PDFs, the key is to first determine whether the file needs to be recognized, and then use a PDF editor to complete the recognition. After recognition, check the numbers and paragraphs one by one, then export to Word or Excel according to the purpose, or save the PDF for further use.
