To add multiple PDF documents, press the 'Add Folder' button on the toolbar. This action will bring up the standard Microsoft Windows 'Browse for Folder' dialog where you can make your desired selection. All PDF documents in the selected folder will be added to your list. If you want to also include the PDF documents in the subfolders of your selected folder, make sure that the Include Subfolders option is selected in the Options menu.
Depending on how many subfolders and PDF documents there are in your chosen folder tree, it may take a little while for TEXTfromPDF to compile the entire list of all of the PDFs. During this time the toolbar buttons and menus will be disabled. You can cancel the add folder process at any time by pressing the Cancel button at the bottom right corner of the main window.