pop up a open-file-dialogue in unity3d

Hello and I'm only a beginner at programming in unity3d.

What can I do to pop up an open file dialogue in unity3d (the file format is .TXT) when I click a button ?

I'm lookin forward to your help

THX!!

The only way to do this with the native file open dialogs is by interfacing with native APIs (which is nontrivial, and requires Unity Pro)

Otherwise, you'll probably want to look into Unity's GUI system to create your own

There is a reasonably nice file browser on the unify wiki at unifycommunity.com

Even if this is not exactly what you are after then this gives you a good starting point for making your own in Unity.