Most failed merges come from one of four causes: a password-protected file, an image format the tool does not add, a damaged PDF or a very large input. The fixes are quick once you know which one you have.
Use the table to find your case, then read the matching section.
On this page
Key takeaways
- A password-protected PDF must be unlocked before it can be merged.
- Only JPG and PNG images are added; other image formats are skipped.
- Image pages take the picture's pixel size, so large photos create very large pages.
- The merged file follows the order of the cards, so check them before you finish.
Steps shown in the video
- Click Choose Files and select the PDFs you want to combine
- Each file appears as a card, in the order it will be merged
- Click Finish when the order looks right
- Click Download to get one merged PDF
Problems at a glance
| What happens | Cause | Fix |
|---|---|---|
| An error appears when merging | A protected or damaged PDF | Unlock it, or open and re-save it |
| An image is missing from the result | Format is not JPG or PNG | Convert it to JPG first |
| Some pages are huge | Photos are used at pixel size | Make an A4 PDF from the photos first |
| Wrong order | Cards were added in a different order | Re-insert with the plus buttons |
| Sideways pages | Original orientation | Rotate before finishing |
| Very slow or stuck | Large files and limited memory | Merge in smaller groups |
An error appears: protected or damaged files
PDFs that need a password to open cannot be merged. If you have the password and the right to remove it, use Unlock PDF and merge the unlocked copy. If a file was cut short during a download or email transfer, it may be damaged. Open it in a viewer: if it will not open there, get a fresh copy.
An image does not appear in the merged file
The tool adds JPG and PNG images. A WebP, GIF, HEIC or other format is left out without an error. Convert the image first with WebP to JPG, HEIC to JPG or PNG to JPG, then add it again.
Some pages are enormous
A picture becomes a page with the same width and height in points as the picture has in pixels. A 4000 by 3000 pixel photo therefore makes a page about 55 by 42 inches. It is fine on screen, but it can make the file heavy and print strangely. Make a neat PDF from your photos with JPG to PDF or PNG to PDF, which place each image on an A4 page, and merge that file instead.
Large inputs
The tool is set for files up to 100 MB each, and the merge uses your device's memory. If the browser becomes slow, merge in groups of a few files and then merge the results. Reduce the finished file with Compress PDF if you need to send it.
Check before you finish
- Every file is unlocked and opens in a normal viewer.
- Images are JPG or PNG.
- The cards are in the right order.
- Sideways cards have been rotated.
- Unwanted cards are deleted.
Need the basics? See how to merge PDF files.
Merge PDF problems: FAQ
Why won't my PDF merge?
It may be password protected or damaged. Unlock it or get a fresh copy.
Why is an image missing from the merged PDF?
Only JPG and PNG images are added. Convert other formats first.
Why are some pages so big?
Images become pages sized to their pixels. Build an A4 PDF from photos first.
How do I merge a protected PDF?
Remove the password with Unlock PDF, if you have the right to, then merge.
The order is wrong. What now?
Re-insert files with the plus buttons, or fix the pages afterwards with Reorder PDF.
Why is the merge slow?
Large files need a lot of memory. Merge in smaller groups.
Does the merge lose quality?
No. PDF pages are copied unchanged.
Can I merge more than two files?
Yes, as many as your device can handle.
Fix the input, then merge
Unlock protected files, convert unsupported images and check the order. Then merging takes a minute.
