OmniDocMerge Scanned PDFs, Then Run OCR Once
Learn why merging scanned PDFs before running OCR saves a step, and how to merge, fix page order, run OCR once and check the result.
If you have a stack of scanned pages split across several PDF files, you probably need to merge PDF files into one document and make the text searchable. The question is which to do first. Running OCR on each file and then merging, or merging and then running OCR, can both produce a usable result, but one order gives you fewer steps and a single set of results to check. This guide explains the order that works well for many scanned sets and walks through it in OmniDoc.
The short version: merge the scans into one PDF first, then run OCR once on the combined file. You end up with one document, one recognition pass and one place to check the text. The steps below show how to do that with the PDF editor in the OmniDoc desktop client, including the checks that catch problems before you share the file.
Should you merge scanned PDFs first, or run OCR first? The short answer
Merge the scanned PDFs first, then run OCR once on the merged file, unless some of the files already have selectable text. The table below covers the common situations.
| Your situation | What to do | Why |
|---|---|---|
| All files are scans with no selectable text | Merge, fix page order, then run OCR once | One recognition pass covers the whole document, and you check one file |
| Some files already have text and some are scans | Check each file, then merge and run OCR on the scanned pages only | Running OCR on text-based pages adds work without adding searchable text |
| Scans are sideways or upside down | Rotate the affected pages before OCR | Recognition runs on the page orientation you give it, so fix that first |
| The set has blank or duplicate pages | Delete those pages before OCR | Removing them first keeps the text layer clean and the page count accurate |
| You need to keep each source file separate | Run OCR on copies, then merge only if you still need one file | Keeping sources apart is useful, but it means more files to track |
Before you start
Before you merge anything, collect the files and check a few things. Each check prevents a rework step later.
- Gather every scan in one folder and confirm the sequence. Merging is easier when the files are named in the order you want, such as "part-01" and "part-02". Without that, you will reorder pages by hand.
- Check whether each file already has text. Open a file and try selecting a line of text. If the cursor selects words, the file has a text layer. If nothing selects, the page is an image and needs OCR.
- Look at the orientation of every page. Scanners often feed some pages sideways or upside down. Fixing rotation before OCR means the recognized text reads in the correct order.
- Note any blank or extra pages. Cover sheets, empty backs of pages and duplicates add noise. It is easier to remove them while the document is still a set of pages you can see.
- Keep the original files untouched. Work on a copy of the folder. If the recognized text needs a second look, you can compare it against the untouched scans.
Merging scanned PDFs and running OCR, step by step
- Install the desktop client if you have not already. Download it from download.omnidoc.top, then open the PDF editor. The web version is for document translation and editing and is not the tool this sequence uses.
- Open the first file in your sequence. This file becomes the base of the merged document, so start with the earliest pages.
- Merge the remaining files into it using the page operations. Add the other scans in order. Merging here combines the pages without changing their scanned content.
- Review the page order and reorder if needed. Scroll through the combined document and move any misplaced pages. Reordering before OCR keeps the recognized text in sequence.
- Rotate any sideways or upside-down pages. Fix orientation now. Recognition works from the page as it appears, so a rotated page produces a jumbled text layer.
- Delete blank pages, duplicates and stray covers. Remove anything that should not appear in the final file. Doing this before OCR means you do not recognize text you will throw away.
- Run OCR on the merged document once. Use the OCR function in the PDF editor on the whole file. One pass applies the same recognition to every page, so the result is consistent across the set.
- Save the output as a new file. Keep the merged, OCR-processed version separate from the original scans so you can go back to them if needed.
Check the result
Once OCR finishes, check the merged file before you share it. Recognition can miss or misread characters, so review the text, especially names, numbers and anything you will quote or cite. Use the table to find and fix common problems.
| Check | How to see it | If it's wrong |
|---|---|---|
| Text is selectable | Select a line of body text on several pages | If nothing selects on a page, run OCR on that page again after fixing its orientation |
| Search finds words from every source file | Search for a distinctive word from each original scan | If a file's words are missing, check whether its pages were included in the merge |
| Page order is correct | Scroll through headings and page numbers | Reorder the pages and run OCR again only if the order changed after recognition |
| Recognized text is accurate | Compare a paragraph with the original scan at the same zoom | Fix paragraph text directly in the PDF editor, or re-scan the page at better quality |
| No pages are missing or extra | Compare the page count with the total of your source files | Check the merge step and remove any duplicate or blank pages you missed |
When you select text across page breaks, the selection should continue smoothly from one page to the next. If it stops at each page boundary, the pages were probably merged without a continuous text layer, and a second OCR pass on the merged file is the usual fix.
❓ FAQ
1. Should I run OCR on each scan before I merge?
You can, but it usually adds work. Running OCR once on the merged file means one set of results to review and one file to keep track of. Run OCR on each file separately only if you need the individual files to stay separate afterward.
2. How accurate is OCR text, and what should I check?
Accuracy depends on the scan. Faint pages, unusual fonts and handwriting are more likely to produce misread characters. Review the text against the original before you rely on it, particularly for numbers, names and quotes.
3. What if only a few pages in the set are scanned?
Check each page for selectable text first. Run OCR only on the scanned pages, or on the whole merged file if that is simpler. Pages that already have text can stay as they are.
4. Can I edit the text after OCR?
Yes, in many cases. The PDF editor can edit paragraph text in place, so you can correct a misread word without re-scanning. Check each correction against the original scan, since editing text does not change the image behind it.
5. What should I do if a page looks wrong after merging?
Go back to the merged document and check the page's order and orientation. Fix the issue there, then run OCR on that page again. Keep your original scans so you can restart the process if needed.
📝 Summary
Merge your scanned PDFs first, check orientation and page order, then run OCR once on the combined file. This sequence gives you one document to review instead of several. Check the recognized text against the original scans before you use it.
