double escape sequence and request filtering is configured on the Web

I have an URL that redirects users to a pdf file. The file contains special character "+" this would prompt an error below

 

Example:

/pdf/tags/cetificate+ version 

 

HTTP Error 404.11 - Not Found 

The request contained a double escape sequence and request filtering is configured on the Web server to deny double escape sequences.

 

I have looked through and noticed that the solution is to set allowDoubleEscaping as True but it would allow people to do HTML Injection, JavaScript Injection or SQL Injection.

 

Is there any way to code in C# to work around this problem? Because I have over 1000+ PDF with these kinds of a special character changing the file name manually will take a long time.

 

Thank You.