To create a sub folder in Procore's Documents tab.
Go to the Company or Project level Documents tab.
Using the file tree on the left, choose the folder you would like the sub folder to appear under. (Note: If you would like to have it appear under your project's folder, select the folder with your project's name.)
Click the orange Create Sub Folder button on the right.
Give your folder a name (e.g. Bid Documents).
Your folder will now appear in the file tree to the left.