In the Documents Dashboard, you have the option to filter your existing documents by their Document Type.
To filter your documents, click on the dropdown menu in the header of your All Existing Documents that begins with Showing... By default, Showing All Documents will be the filter selected. From here, you will have the option to filter all of your existing documents by their Document Type.
For example, if you wish to only view your existing Requirements Documents, click on the Requirements Documents Only filter. You will then be shown only existing documents of your selected type, and your filter drop-down will now say Showing Requirements Documents Only (or whichever Document Type you've selected) at the top of your view.
If you wish to go back and view all of your existing documents, simply select the All Documents filter to return to your default view.