The Digital Downloads Importer Plugin allows you to easily bulk import .pdf, .zip, .odt and any other file type, excepting jpgs*.
If you’re tired of uploading digital products one at a time, Digital Downloads Bulk File Importer for WordPress is exactly what you’re looking for. Use the streamlined interface to make setting up your store painless. For more information read the readme
*jpgs are used for product and post images. You can already upload them easily, but allowing them via the plugin would cause conflicts.