As I can understand, you want to have web part on document template in each new document (you creating new document go to design and configure web part witch is already there right?)
So you have to approach:
1.Create new layout - it defines you web part zones. Then create new template which use this layout, and add there web parts. In general tab select clone template as ad-hoc. Go to your document type and set this template as a default template (general tab).
2.Add fields on document type and write a transformation. Create layout and template like above but don't add web parts. Add repeater and configure it to display your document according to your transformation. Set template as default in your document type.