Kindly Refer below KM document and see if it helps !!
E-BI/XMLP: Is it possible to have a Digital Signature in PDF Reports PeopleSoft BI/XML Publisher? (Doc ID 876893.1)
you cannot use multiple signatures on the same BIP Report, just one single one. However, you can implement logic via the delivered interface class, to determine which digital signature amongst multiple signatures that may be defined in the PeopleSoft keystore, is to be used at runtime based on the runtime data
Digital signature is documented in the BI Publisher PeopleBooks, this section:
Also refer to the section that goes into the details of the delivered IPT_PDFSIGNATURE_INT:IPDFSignature interface class, if the customer has multiple digital signature that could potentially be used for signing, and wants to specify logic to determine which signature to use to sign the report based on runtime data.
This is documented in this section of the peoplebooks: