How to create custom logic that checks custom field in billing document item

Hi,Experts,

I am searching how to create custom logic that checks custom field in billing document item.

But I cant find Badi that do it.

Is it possible to create custom logic that checks custom field in billing document item?

If it is possible,would you be so kind to tell me how to do?

Thank you,

Best regard,

Takahiro Yamauchi