How to identify changed rows in BBP_DOC_CHECK_BADI ?

Hi Experts,

I have a requirement to give an error message if a row is changed in SRM PO for which some custom fields are marked. We need to identify the changed rows in the DOC check badi for this purpose, how to achieve?

Do we need to export the data from DOC_CHANGE to DOC_CHECK? or there is any better mechanism?

This may be a silly question, however, any leads would be helpful.

Thanks

Mohit