How do I set config file in root dir to load the DLL

Question

I have a dll (Custom Pdf handler) which is bin dir of my application which takes raw url and concate the url with the file server name and downloads file.
My file server and web server are in separate box. So what i did was on click of link I send the request to the web server which has my custom handler which knows
which file server to go and download the file. But the handler dll is in bin directory of application. so my root directory config does not know
how to load the dll.

 

<system.webServer>
<handlers>
<add name="PdfFileHandle" path="*.pdf" verb="*" type="FileHandler.FileHandler" resourceType="Unspecified" preCondition="integratedMode" />
</handlers>
</system.webServer>

I added file handler in configuration file of root but it does not know how and where to get the FileHandler.FileHandler