Displaying PDF document

Hi there, I am currently working on a project where you can upload and view a PDF document. So far I have the upload PDF function completely working. The only issue I am having is when I click on my View LinkButton I get an error: "Input string was not in a correct format.". I feel as though my LinkButton is properly linked but the error occurs when it hits: 

int id = int.Parse((sender as LinkButton).CommandArgument);

Also, when I use: //var id = ((LinkButton)sender).CommandArgument;    instead, I'm not getting errors, but nothing is showing up.

 

The code for my LinkButton is shown here: 

 

 

Any help would be GREATLY appreciated!

Thanks you,

M