Insert attachment (PDF doc) into workflow

Hi.

I want to insert an attachment into a workflow. Via a webpage, the user upload the file (BIN format) and call a RFC. This RFC must start a workflow via an event. I think i can get the workitem so then, i can attach the BIN to the workflow.

Finally, the approver will have this document in the Business Workplace.

My problem is that i'm in a 4.6c SAP version and must use SO_DOCUMENT_INSERT or similar. Another problem is that i don't know if this function module is the correct one and also don't know how to fill its parameters.

Thank you for your help.

Kind regards,

Inigo.