I’m making an assumptions based on the information in your entry, when you say document type, you are referring to wt.doc.WTDocument object.
FYI, OOTB the Approval Process workflow is started in the “In Work” state in the Approval Routing lifecycle. Also, OOTB the lifecycle for wt.doc.WTDocument is the Basic lifecycle.
If you truly want to assign the OOTB Approval Process workflow to a document when it is created, in the initial state of the advanced lifecycle you assign to wt.doc.WTDocument (document), set the Approval Process workflow to start in its Phase Process.
Caution; if you decide to have wt.doc.WTDocument (document) continue using the Basic lifecycle, understand that OOTB the Basic lifecycle is also assigned to wt.part.WTPart (part) object. So, if you modify the Basic lifecycle and change it to become an “advanced” lifecycle and have the Approval Process workflow started in the Phase Process of “In Work” state without changing the lifecycle assigned to wt.part.WTPart, the Approval Process workflow would kick off on the creation of a document and a part.
Suggest you create a new advanced lifecycle and in the initial state in this new advanced lifecycle, assign the Approval Process workflow to the Phase Process. In the appropriate Windchill context (Site, Organization, Product, Library) create a new OIR which assigns your new lifecycle to your document type.
To define the participants to be assigned to the Reviewer and Approver roles during the creation of the document would require a customization. Rather than customizing Windchill, why don’t you use the Setup participant functionality in an assigned activity in a workflow to assign the participants to the Reviewer and Approver roles?
