Thanks for the response.  But  I do need some clarifications on your statement  
"you can use a standard publishing feature in which case they would need the private publish URL in order to access the published content "
Please explain more on this statement.  And I would like to test it out before we purchase your product. 
What we want are 
1. Upload a file to DriveHQ folder
2. Make it as a URL and email our client to download the file using this URL.
Each client would have a UNIQUE file to download,  using a UNIQUE URL
 
We need you to explain the step 2. " Make it as a URL "    --- How do we do this ?   
How do we publish it ?  Do you have a template or buttons on your website to help us to publish it ?
As you see that FileFactory.com  has this facility where you can upload a file and they make a URL link to that file
so that other people can download the file via that URL .
But we won't be using FileFactory as we were advised by many of our business asssociates.