Why Won't My PDF Files Merge?

PDF files usually will not merge because one is password protected, damaged, or not a PDF, or the batch goes over 20 files, 200 MB, or 500 pages.

Merge PDF marks the problem file on its card and disables the Merge Files button until that file is removed from the list.

Read the message under the button, because it names the cause.

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Password-Protected Files

A PDF that needs a password to open cannot be read, so it cannot be merged.

Its card shows a Locked badge with a lock icon, or the text "Password protected" on a phone screen.

Under the button, a message reads "Some files are locked or damaged; remove them."

Merge PDF has no password field. If you know the password, remove the file from the list, unlock it with Unlock PDF, and then add the unlocked file back to Merge PDF.

If you do not know the password, ask the sender for a copy without one.

Some PDFs open without a password but carry permission restrictions, for example a ban on editing.

Their cards look normal, but the merge stops with a message such as "PDF 2 is locked; unlock it first." The number tells you which file in the list is the problem.

The message panel offers an Unlock PDF button, but that tool needs the password set by the document's creator, and the file must be selected again there.

If you do not know the password, ask the sender for an unrestricted copy.

Damaged or Unreadable Files

A file whose structure cannot be read gets a Damaged badge, or the text "Can't be read" on a phone screen. Common reasons:

• The download did not finish or stopped partway, so the file is cut short.
• The file is not a real PDF, for example a photo or another document renamed to .pdf.

Try downloading the file again or ask for it to be resent from the source.

Some damage only shows up while the merge is running, with a message such as "PDF 3 is invalid or damaged."

The message panel then offers a Repair PDF button that opens Repair PDF to try to recover the file structure.

Files That Are Not PDFs

Merge PDF only accepts PDF files.

The file picker only shows PDFs, and other files dragged onto the file box are rejected with the message "Format not supported:" followed by the file name.

Convert other files to PDF first, then merge the results.

JPG photos can be converted with JPG to PDF, PNG images with PNG to PDF, and Word documents with Word to PDF.

Going Over the Merge Limits

One merge has the following limits, and each one has its own message:

• At least 2 files. With one file, the message reads "Select at least 2 files."
• Up to 20 files. With more, you see a message such as "The limit is 20 files; remove 1."
• 200 MB in total. Above that, the message reads "Total size is over 200 MB; remove some files."
• 500 pages in total. Above that, you see the message "Up to 500 pages; remove some files."
• Up to 500 pages per file. A message reads "A file has more than 500 pages; split it first with Split PDF."

A file over 500 pages gets a Too Long badge, or the text "Exceeds the page limit" on a phone screen.

Divide it with Split PDF, which can open documents longer than 500 pages, then merge the parts you need.

For the 500-page total, use Custom Range mode and enter only the pages you need from each file. Only the selected pages are counted.

For the 200 MB limit, shrink the largest files with Compress PDF before merging.

This total limit is the same on phones and computers, so switching devices does not change it.

When the Merge Fails While Running

Merging runs in your browser and uses your device's memory. If memory runs out, you see "Out of memory; close other tabs or use a computer."

Large files also get a warning that processing may be slow, starting at 32 MB on phones and 64 MB on computers.

If you see "Couldn't merge the PDFs; try again.", press Try Again, then Merge Files again.

Your file list and its order are kept, so you do not need to select the files again. Close other tabs before retrying if the files are large.

Not a Failure: What Changes After Merging

Some changes in a merged file come from how the tool works and do not mean anything went wrong:

• Digital signatures are no longer valid. You can still merge, but ask for the document to be signed again if the signature needs to be valid.
• Forms and bookmarks are not carried over. If recipients still need to fill in a form, send that form as a separate file.
• The document title comes from the first file. The title and author in the merged PDF's properties are taken from the first file in the list.