How to associate a part to a document

My requirement is -

there is a soft attribute in my document creation page called drawing number.

This drawing number will take part number as input.

Then it will associate the part with the document.

I have been able to craete the link, the document is shown under Details Page of the Part under Related object tab->Described by Document where as my requirement is

the part should be shown in Document Details Page->Related Objects tab->Describes Parts