OmniDocHow to keep bookmarks after merging PDFs
When merging multiple PDFs, the bookmarks (table of contents navigation) of the source files are often lost or misplaced. This article explains what to check before merging, how to check after merging, and how to remedy missing bookmarks.
Key points of this article
- Before merging, first confirm whether the bookmark exists and whether the hierarchy is complete in the source file. This is the basis for judging whether subsequent remediation is necessary.
- Whether the bookmarks are retained after merging must be opened one by one to check, not just the number of pages and page order.
- The bookmark points to the page number. Once the page order changes, the bookmark may point to the wrong page. The order needs to be determined before merging.
- When bookmarks are missing, you can manually add them by chapter in the bookmark panel of the reader, which saves time compared to rearrangement.
When combining several PDFs into one, the order of the pages is usually correct, but the bookmarks are easily lost. A 30-page paper with appendices, a 12-page contract with a supplementary agreement, and after the merger is opened, the table of contents navigation on the left is empty, or only a few items from the first document are left. Readers have to scroll from page to page to find chapters.
A bookmark (also called an outline or table of contents) is a navigation tree in a PDF, with each entry recording the title and the page number it points to. When merging, the page number of the bookmark needs to be recalculated along with the page. Some merging methods will directly discard the tree, and some will only retain part of it. So the key to this matter is not the page itself, but the handling of the bookmark structure before and after merging.
This article talks about two things: what needs to be confirmed before the merger, and how to check and remedy it after the merger. After reading it, you can decide whether your file needs special treatment, and you can also know where to start if the bookmark is missing.
Should the bookmarks be retained during merging? One sentence conclusion
Whether you need to handle bookmarks when merging PDFs depends on whether the source files have bookmarks and what the merged files are used for. The table below can help you locate quickly.
| your situation | Recommended practices | reason |
|---|---|---|
| The source file itself has no bookmarks | Merge directly without additional processing | There is no navigation tree to keep, and there are no directories to check after merging. |
| The source file has complete chapter bookmarks, which can be used for reading after merging. | After merging, check items one by one, and fill in missing items manually. | Bookmarks are the main entrance to reading navigation, and losing them will significantly affect search efficiency. |
| Splicing of multiple independent documents (such as contract plus attachments) | Create a first-level bookmark for each file, with the name corresponding to the file name or attachment number | Readers search by file rather than by chapter, and the first-level bookmarks are clear enough |
| After merging, you still need to continue editing or distributing | Unify page numbers and order before merging, and then check bookmarks after merging. | If the page number changes, the bookmark pointing may be misplaced. The later you find out, the more troublesome it will be to correct it. |
Before you start: Confirm these points first
Before merging, taking a few minutes to check the source files can avoid having to rework after discovering problems after merging.
- Confirm whether each source file has bookmarks. Open the file in Reader and view the bookmarks or table of contents panel on the left. If the panel is empty, the document itself has no bookmarks and cannot be retained during the merge.
- Check whether the bookmark hierarchy is complete. Some files have only one level of entries, and some have three or four levels of nesting. The more complex the hierarchy, the more necessary it is to check it level by level after merging, because sub-items are more likely to be missed.
- Determine the merge order. Bookmarks record page numbers. Once the order is changed, the bookmarks will change accordingly. Arranging the files in reading order first before merging them can reduce subsequent adjustments.
- Determine whether the file is a scanned copy. If the bookmarks of the scanned PDF are from the original file, they will still exist after merging; if there are no bookmarks, you can use OCR to identify the text first, and then manually create navigation by chapter. The judgment method is very simple: try to select a piece of text in the reader. If you cannot select it, it will usually be a scanned image.
- Back up original files. Merging and adding bookmarks will generate new files. Keep the originals to return to the starting point in case of errors.
Steps to merge PDFs and check bookmarks in OmniDoc
The following steps use the OmniDoc desktop client as an example. If it is not installed yet, you can download it from download.omnidoc.top.
- Record bookmarks in the source file. Open each PDF with a reader, take a screenshot or write down the first-level and second-level entries of bookmarks, and merge them for comparison.
- Open the PDF editor of the OmniDoc desktop client. Import the files that need to be merged and arrange them in reading order.
- Use the merge function in page operations. Combine multiple PDFs into one and check whether the pages of each document are included to avoid missing appendix or last few pages.
- Export the merged PDF. Export as a new file, do not overwrite the source file, the file name can be added with date or version number.
- Open the results in Reader and view the bookmarks panel. Compare the records in the first step to see whether each entry is still there and whether the level is the same as before.
- Click the bookmarks one by one to check the jump page. Click on an item to confirm that it jumps to the correct page, especially the items before and after the splice, which is prone to errors.
- Missing or misplaced bookmarks are manually added. In the bookmark function of the reader, jump to the corresponding page, create a new bookmark and fill in the title, and nest according to the original level.
- Save the updated file. Make sure the bookmark still exists when saving, and reopen it to confirm that the added content has been written to the file.
Check each item after completion
Once the consolidation and additions are complete, don’t just look at the page count. The following check items can be ticked one by one.
| Check item | What do you think? | What if there's a problem? |
|---|---|---|
| Does the bookmark exist? | Open the bookmarks panel of the reader to see if there is any content in the panel | When the panel is empty, go back to the source file to confirm whether there is no bookmark in the first place, and then decide whether to build it manually. |
| Is the number of entries consistent? | Compare the number of primary and secondary entries recorded before the merger | If there are any items missing, please add them on the corresponding chapter page. |
| Is the level correct? | See if the child entry is indented below the parent entry | If the hierarchy is out of order, you can drag and adjust it, or delete it and rebuild it. |
| Whether the jump page number is accurate | Click one by one to see if it falls on the page where the title is located | The page number offset indicates a change in the merge order or the number of pages. Go back to step 3 to check. |
| Is the splice normal? | Focus on checking the bookmarks near the first and last pages of each document | The items at the splice are usually easily misplaced and can be corrected separately. |
| Whether the file can be opened normally | Reopen the saved file with a reader | If abnormal, re-perform the merge with the original file |
# Core comparison
There are roughly three common ways to merge and retain bookmarks, each of which is applicable in different scenarios.
| Practice | Applicable scenario | Matters needing attention |
|---|---|---|
| Check item by item after direct merger | The bookmark of the source file is complete and the number of pages does not change much. | The workload is small, but you have to click to check every jump. |
| Manually build bookmarks after merging | The bookmark is lost in the merge, but the structure of the original file is clear | It takes time, and the results are manageable. |
| Split and then merge | Precise control of chapter structure is required. | There are many steps to do, and use only when necessary. |
# which method is suitable for you?
If you are a student or researcher, merge papers and appendices, bookmarks are mainly used to jump to chapters and references, it is recommended to directly merge and check them one by one, and the missing chapters can be rebuilt manually.
If you are dealing with contracts and attachments, and the boundaries between documents are more important than chapters, it is recommended that you bookmark each document with the same name and attachment number, making it more intuitive for readers to find it.
If the merged file is to be preserved or distributed for a long time, it is recommended that all checks be completed before saving, and the control record of the source file and the merged version should be kept to facilitate later modification.
# frequently asked questions (FAQ)
1. After merging PDF, all the bookmarks disappear, can you still get them back?
Once the bookmarks in the source file are discarded at the time of the merge, they usually cannot be recovered directly from the result file. It is safer to re-merge with the original file and then manually build it in the reader according to the chapter.
2. Why is the page number of the bookmark offset?
The bookmark records the page number, and when the page order or the total number of pages changes after the merge, the page number will not match. Determine the order before merging, and then check the jump one by one after merging, so that the offset can be found in time.
3. What about the bookmarks of the scanned version of PDF?
If the scanned piece itself has a bookmark, it will generally be retained after the merger and only need to be checked. If you do not have a bookmark, you can first OCR the scanned part to identify the text, and then manually establish the navigation according to the chapter title. The results of OCR recognition need to be checked, especially the key contents such as title and page number.
4. Does the merged file need to be retypeset?
The main purpose of merging is to put the pages together in order without changing the layout of each page. If the page size or orientation of the source file is inconsistent, it may appear inconsistent after the merge and can be adjusted in the page operation before being exported.
5. Is there a free tool to merge and retain bookmarks?
When choosing free tools, you can first look at several aspects: whether there is a limit on file size and number of pages, whether there is a watermark on the result, whether the file will be uploaded to the server, and whether bookmarks and typesetting will be retained after the merge. No matter which tool is used, it is recommended to use the checking method in this article to check the results.
# Summary
The key to keeping bookmarks after PDF merging is to confirm the source file structure before merging, check the jump item by item after merging, and reconstruct the missing parts in time. By ordering the pages and keeping the original, you can avoid most of the rework. When merging PDF, the integrity of bookmarks often determines whether the reader can find the content quickly, and it is worth taking a few minutes to check carefully.
