This tab of the Sales Payment Terms Adjustment form provides general information about the change in payments terms used for a specific document: Invoice or Customer Order.
The Sales Payment Terms Adjustment (create) form. The Main tab
...
In the Document field, you can select the document to which the original payment terms were applied. Click the For this, to the right in the field, click the 
(ellipsis) button to open the Select Data Type dialog box.
The Select Data Type dialog box
In the dialog box, select the type of document and then, in the next dialog box, select the particular document of this type. Close the dialog box.
...