Create PDF Portfolio via API with signed and unsigned files

Hello Team,

hope you can help me.

We want to create a PDF collection via the API, to receive in the end a portfolio with signed and unsigned pdfs.

at the moment we use the combinePDF process. the process will be initiated but on polling the status we receive an error

"Source PDF is signed and cannot be processed.; transactionId=xxx"

whats our mistake?

Is there a different command for creating a portfolio?

Using the same files in Adobe Acrobat it is fine.

Thanks for help!