Make material as a mandatory field for a particular document type in PR

Hi,

Currently we are in SAP 4.6c version. There is a business requirement for making material as a mandatory field for a particular document type of purchase requisition as they don't want the user to raise non material purchase requisition using that document type. The field for material is currently not available in the configuration for Define Screen Layout at Document Level for purchase requisition.

So could you kindly let me know the possible options to prevent user from raising a non material purchase requisition using that document type. If not could you kindly suggest me the user exits available at the time of saving purchase requisition which i could use so that we can write a code to check if the material number is entered or not. If not entered prevent the user from saving the purchase requisitions.

Also it would be helpful if you could let me know how the fields for enjoy transaction (like material,document type) can be made available for selection in the configuration for Defile Screen Layout at Document Level for purchase requisition.

All you help in the solving the above problem is highly appreciated.

Thanks & Regards

Ram