come al solito, basta leggere la LORO documentazione:
Can I edit the PDF template(s)?
Yes, of course.
If you want to change Font Family or Font size, or margin top-right-bottom-left and so on you can do it in config page.
If you ant to edit the layout, VIM uses a file we call template to produce PDF documents. You can edit the appropriate file for invoice and/or delivery document but you need TCPDF language knowledge.
Before you start to edit those files, please note that we don't give support (even to the project supporters) for programming languages or library developed by third party.
Pdf's template files are located in:
www.yoursite.com/administrator/component/com_vminvoice/pdf/temp/