Invoice Automation- How to restrict documents in web center content imaging

We are trying to restrict documents other than invoices from getting converted into invoices using IDR. Example: Supplier are sending Invoices & other related document like purchase orders, drawings, contracts, packslip, etc. IDR is scanning all the documents & trying to create invoices for all the documents/attachments in webcenter. AP Invoice Import rejects these documents which can be seen in the scanned invoice infotile. We would like to understand how we can restrict these documents in first place even before it is imported into Web center. We made changes in Web center content imaging application to restrict other documents.