Will merging a digitally signed contract with other files break its signature?
Yes. A digital signature is tied to the original file exactly as it is, so any new file built from its pages, including a merged one, cannot carry a valid signature. [[merge-pdf]] shows a warning when it detects a signature, and the fix is to send the signed contract on its own, or merge the documents first and sign the merged file.
What a digital signature actually protects
A digital signature is not a picture of your handwriting. It is a mathematical fingerprint of the whole file, sealed with the signer's certificate. When the other party opens the contract, their software recalculates the fingerprint and compares. If anything in the file has changed, the check fails, and that is precisely what makes the signature trustworthy.
Merging builds a brand new file containing the contract's pages plus others. The image of the signature or stamp may still show on the page, but the digital check will not pass, so the recipient's reader shows the contract as unsigned or the signature as invalid.
How the tool warns you
As you add files, the tool looks inside each one for the markers a digital signature leaves. When it finds them it shows a warning naming the file: it appears to contain a digital signature, and any modification may invalidate it. The warning does not stop you merging, because you may want a read-only copy, but it tells you the result will not be a signed document.
The right order for your situation
- The contract is signed by both sides and you need to send it with attachments: send the signed contract as its own file and merge only the attachments into a second one.
- The contract is not signed yet and you want it together with its schedules: merge everything first in Merge PDFs, then send the merged file for signing, so the signature covers every page.
- You only need an internal archive copy: merging is fine, but keep the signed original, because it is the only copy anyone can verify.
The second route is better for both parties anyway: one signature over the complete file means nobody can later swap a schedule without the signature breaking.
Common questions
Does the same apply to a scanned signature image?
No. A signature image is part of the page content and travels as it is. Only a certificate-based digital signature is invalidated.
Could the tool miss a signature?
The check looks for known markers inside the file, so treat it as a helpful signal rather than a guarantee. If you know a file is signed, act on that.
Is this legal advice?
No. It is technical information about how signatures work. For legal questions, ask a qualified adviser.