Needs more intuitive UI. For example instead of using the move up/down buttons, having drag/drop to rearrange the list would be more helpful.

There are a few improvements that could be made into UI. Improvement list
1) Already mentioned, multiple selection in the add menu.
2) allow multiple selection in the File List where the user can drag/drop image files. This will allow the user to remove only selected files.
3) allow the removal of selected files instead of just clean button. If the user has a large number of files in the list and wants to remove a few of them it would be annoying fto select each and remove them 1 by 1 since the file list changes with each removal, the user will have to find the image each time.
4) allow an option only exporting only a selected number of images at a time.
5) display a small iconic representation of the selected file.
6) Remove "Buy Now" button after the user has registered the software.
7) remove un-needed "Exit" button as it can result in accidental exiting of the program.
8) Instead of using "Add Folder" button, allow the selection of folders in the selection window that is displayed when the user presses "Add"


Most Importantly:
Do NOT do conversion of the image to PDF conversion in the user Thread. Create a separate thread of the conversion and show a progress bar. This is very very important because the program is currently resulting into a non-responding state as it does its work which can be a long time depending on the number of images and their size