You may have noticed that when you add attachments to your exports, the margins for the attachments are larger than for the rest of the export. 

This is because the attachment is seen as an image, not text, and needs to be scaled down to make room for the header and footer of the export. This means that the margins of the export style are added to the margins of the attachment.

Unfortunately this means that it's not possible to completely eliminate the margins, ever.

The workaround we offer is to either make the margins of the style smaller, which will affect the entire export, or make the margins in the original document used for the attachment smaller. 
We recommend the second option.

In the style settings this is the field that would need to be adjusted if you choose the first option: