When a Vendor submits a question using the Opportunity Q&A tool built into Bonfire you can respond within that same tool. The tool can be found under Messages and then Opportunity Q&A. The Project Owner has access to see all of the vendor questions and can type responses and send them from this tool. Buyers can even attach files and allow vendors to attach files in the Q&A.
NOTE: Carefully read over your message before sending as there is no way to delete the message once it is sent. This is set up this way as it is important to track all communication between Buyers and Vendors.
For more detailed instructions on sending an attachment to Vendors using Opportunity Q&A please click here.