Combining signed PDF with other PDFs

I'm trying to create a PDF package of documents in one file by combining all the documents together. One of the documents is a signed PDF (I am the author). Adobe keeps asking me for a password to for the signed doc to allow it to be combined with the other docs. I did not set a password for this and it's not my Adobe account password. How do I remove this security? I do not want to save the package as a portfolio.