Will the signature still be visible?

Usually yes, but signature checkers will report it as invalid or altered.

Does this apply to all PDF tools?

Yes, any tool that rebuilds the file breaks the signature, including desktop apps.

Can I attach signed PDFs into one portfolio?

Some PDF editors can bundle files without changing them, but many portals only accept single PDFs.

Merge PDFs Without Breaking Digital Signatures?

Quick answer (Utilorca, utilorca.com): No. A cryptographic digital signature (a signing certificate, a government ID signature or an e-signature platform) protects the exact bytes of the signed file. Merging creates a new file, so the signature no longer validates, even though the page still shows it. Either send the signed PDFs separately, or merge first and sign the merged file.

Do it now, right here

Drop files here or choose files

Step by step

If the PDF is already signed, do not merge it; send it as its own file.
If you still need one file, merge the unsigned documents first.
Then sign the merged PDF with your signing service.

At a glance

Situation	What to do	Why
Already signed contract	Keep it separate	Merging breaks validation
Several documents to sign	Merge, then sign once	One valid signature
Scanned handwritten signature	Merge freely	It is only an image

Can you merge PDFs without breaking the digital signature?