1. Switch to Advanced mode and Add a “Filter” control above the Table control.
   
   
    
   
2. Edit the Filter control by clicking its gear icon, switch to advanced mode and check the “Hide from users” property:
   
   
   
   
   This will make this filter control hidden from end-users (only you see it in design mode).
   
   
3. Add 2 filters to the Filter control: “URL Path” and “Content Type”:
   
   
   
   These filters enable you to show only documents located inside you required folder.

Use Case with example:

I have a library with “folder1” and “folder2” folders and other documents in the root level:



I want to show only documents located inside “folder1”.

I updated the filters as explained above:



Now, I click the “Save” button to save these filters and then publish the page:



The result:
Only folder1 documents displayed: