It's common for many RFPs to contain some documents for Vendors to sign, scan and reattach somewhere in their final submission.
If you want to attach a file for your vendors/proposers to view (or use), you can attach that in the text editor of the Section body. Simply click your cursor squarely on the Section Header, which will then highlight in grey. Underneath the Section Header will be text Click here to write Section Overview which will open a Text Editor option for you to add any read-only clarifications or attach a document or file.
The vendors who are viewing your RFP will have the ability to open and/or download your attachments.