To know how to use all the functionalities of the Supplier portal, have a look at this article: http://help.lsp.expert/en/articles/3340222-getting-started-with-the-supplier-portal
To unshare a file you shared with a supplier, you have two options:
1) In the Files tab of the job, it the file is shared with all your suppliers, you can click on the three dots at the end of the line of the file and then click on Remove sharing with all suppliers.
2) In the "Files shared with the supplier" panel in the outsourcing page of the job, you can click on Unshare next to each file.
