1. Order could contain products from Multiple vendors, Would you like to add address of all the vendors? 2. Vendor Address is optional, what you what to do if the vendor address does not exists?
In 'PrintOrdersToPdf' function of \Libraries\Nop.Services\Common\PdfService.cs file under address section get vendor address using VendorId, If vendor Id is not provided you could get vendor Id from order Items. Once you have Vendor Id you could get vendor information and vendor address using below code. var vendor = _vendorService.GetVendorById(vendorId); if (vendor != null && !vendor.Deleted && vendor.Active) { var vendorAddress = _addressService.GetAddressById(vendor.AddressId); } Code sample for adding address in pdf is available in 'PrintOrdersToPdf' function.