Once you accept the replies received against the RFQ then Purchase order is created automatically.
Please follow following steps:
Accept request for quotation replies
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Use this procedure to accept lines in an RFQ reply from a vendor.
1. Click Procurement and sourcing > Common > Requests for quotations > Request for quotation replies.
2. Use the filter options to search for the RFQ reply that you want to accept. For example, type a vendor account number in the Vendor account field.
3. In the Request for quotation replies list, select the RFQ reply to accept.
4. On the Action Pane, on the Reply tab, click Accept.
5. In the Posting request for quotation acceptance form, in the lower pane, select the lines in the RFQ reply that you want to accept.
6. Click Parameters, and then, in the Reason accept field, enter a reason code. To defer specifying a reason for accepting the RFQ reply, select the Late selection check box. For more information about reason codes, see Reasons (form).
7. Click Print, and then select the Print request for quotation acceptance check box to print the RFQ acceptance sheet.
8. Click OK to update the RFQ reply and to print the RFQ acceptance sheet. An RFQ journal and a purchase order are created automatically based on the accepted lines in the RFQ reply.
The lowest status for the RFQ reply changes to Accepted, and the highest status changes to Accepted.
Please verify following links
technet.microsoft.com/.../gg242501.aspx
technet.microsoft.com/.../hh209537.aspx
I did not find any technical documentation related to this..
If you need technical details about Auto-Purchase Order creation, may be we need to do some debugging of the process to find out the details.
Please let me know if you need those details.