Modify Invoice

installed nopCommerce and its very complicated trying to understand how I edit the layout of the invoice.
I have read that I need to download the source, edit that and recomplie.

I downloaded the source, edit the pdfhelper.cs file, did a recompile and am lost after that. What file do I now upload and to which directory?

If anyone could help, it would be appreciated.

Upload Nop.BusinessLogic.dll from/to /bin/ directory

Thank you.
I managed to edit the Invoice and the other stuff.

System is really cool. But I wonder how does it stack up against Magento where you can manage more than 1 store.
Is this coming on the next release?

Multistore functionality is on the roadmap of nopCommerce.

Talking specifically about next version i.e nopCommerce 2.0 - This feature won't be available in 2.0 version since 2.0version is coming out in MVC version which will be the major enhancement in 2.0 release.