In Demandstar you have the ability to post an internal bid response on behalf of a vendor/supplier. 

First step would be to search for the supplier within the Bids Planholders tab shown below:

Email would be the best option to search - if the supplier does have an account tied to the email they would like to use, you can then select them from the list after you select search and find the account. 

If the supplier does not have an account tied to the email address they would like to use, you can then chose the option to create a supplier account for them with their desired email.

PLEASE NOTE - do not create a supplier account with the suppliers email as a first step - if they already have an account tied to that email address and another account is created with the same email, this will cause a system error in which their account will be duplicated and they will not be able to access anything tied to the duplicate account as well as anything tied to the bid.

Please search for the supplier first to ensure there is no account tied to the email address they want to use for Demandstar before making them a new account. 

After the supplier is added to the bid, you can then choose the Add Response option shown below:

Next select the supplier from the drop down list. This will then allow you to upload the files on behalf of the supplier and if this is done correctly they will be able to access it with the same email address/account used in the search or create option.