Consuming the SOAP webservices from SAP for PDF Assembling/Commenting/Watermark

We got the SOAP WSDL File for PDF Assembling/Bookmark/Commenting and we are trying to consume the web service from SAP ABAP.

Details:

• When calling the Invoke Method of the PDF Assembler, system is giving Conversion Error.
• The PDF Contents which are attached in the application are passed to the Invoke Method in XSTRING format.

Please help on this, if anyone worked on calling the PDF Assembler web services from SAP.