Adobe Form: How To get image from GOS and use it in a PDF

Hi,

I want to show an image in a PDF-form.

The image is stored via TX FK02 as a attachment to the vendor.

(This is called GOS, Generic Object Services)

In the Form I know that the Image must be a field type XSTRING.

It is clear how to do it in the form.

But it is not clear how to do in the abap-pgm.

Which tables are involved and how can I read this to convert it to XSTRING that I can use it in the form.

Thanks.