Source of Drawings
The Source of Drawings panel allows you to specify the source from which you wish to populate the Drawings to process panel.
The "Database" tab is shown by default, with the "Database" tab selected, the drawings to process tree shows the drawings available to you in your current project.
Selecting the "HDX file" tab changes the view
Here you specify and input and outut location, either with the button or by entering/pasting in the folder location. Note that the input/output location can be the same folder, which will enable the "I confirm that I want to override the input HDX files" checkbox, enabling you to replace the HDXs once they have had the batch operations run on them.