As a Buyer, you can easily see a project from a Vendor's view without having to register for a Vendor account if the project is in the Pending or Open stage.
From your Project Details page, go to the Actions button in the top right-hand corner.
Once you click on Actions, a drop-down menu will appear. Select Preview on Portal:
This will bring you to the Opportunity page that is visible to the Vendor for this Project:
Under the Supporting Documentation section, the Vendors will have access to download all of the Public Files that you have uploaded.
The Requested Information section will contain all of your Requested Information and will allow the Vendors to download a copy of any Questionnaires and/or BidTable templates that you have created for this project.
Lastly, the Messages section will show the Vendors all of the Public Notices posted by you and/or allow the Vendor to send you a question via the Opportunity Q&A tab if you have Questions enabled for the project.
However, since you are logged in as a Buyer you will not see the Create Submission button (which takes the Vendor to the Upload page) that would normally appear for the Vendor at the very bottom of the page.