@csmwebdesign. Thanks for using my plugin. Your last post provided a lot of vital information. I think that your problem is not only the issue with being on Windows and the DS being a backslash instead of the forward slash. Your issue seems to be either that you are using backslashes in the Plugin Manager 'Location of the Listing Folder', or that what you are typing backslashes in your article, and your Article's WYSIWYG editor is converting them to '%5C' through URL encoding. To check it, toggle (or turn off) your editor, and see what it says.
What you should have in your article is: {easyfolderlistingpro folder='documents/Medical_Students/Feedback'}
From what I see in your post, you have: {easyfolderlistingpro folder='documentsMedical_StudentsFeedback'} which gets converted to http://localhost/documents%5CMedical_Students%5CFeedback/Feedback.pdf with URL encoding applied by the WYSIWYG editor. %5C is the URL HEX code for backslash ''.
Also, note that the two 'DS' that you changed to '/' in the php file corresponds to the / just before Feedback.pdf, which works as you can see from your post.
So, please double check whether you have any backslashes when you specify the listing folder.