Access local files from internet like peer-to-peer

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C#

Javascript

.NET

PHP

MySQL

jQuery

Hi,
I need some pointers, I'm need to create an C# app that will WATCH a folder in a PC and insert the new files to a MySQL database in a remote webserver, the tricky part is that I need the C# app to allow the user in the PC to access these files in the local folder from the Web server so they can open them, and we are not talking about just transferring the file to the webserver, just open it directly from the local folder, and keeping in mind that the local PC is behind a router, all normal ports are closed, so it will need to be like a peer-to-peer connection I think, but the "client" peer is not a PC is a website running on PHP, IIS should not be required, but we can create services in Windows if they are needed.

This C# app will be running in the system try all the time.

Is this possible to create?, I've seen apps that can do similar things, but don't know what is required.

Thanks in advance.