Dear Anupam,
Before posting the query please google it.
Anyhow Below is the solution for your question if i understood your requirement.
If you want to trigger you custom workflow when the PR is created/changed.
BUS2105 is the business object for PR. Open this BOR in the tcode SWO1.
In that BUS2105 you can find many methods use anyone as per your requirement.
You can also create custom methods and logic in this BUS2105 through Delegation concept.
To trigger the workflow map this BUS2105 and its method in the header details of the workflow.
So when you ever PR is created your workflow will trigger automatically.
You can also trigger WF manually from custom program using FM SAP_WAPI_CREATE_EVENT by passing BOR and its method which you mapped in workflow header details.
Reward points if helpful!!!
Thanks,
Anand
Message was edited by: Moderator