Client Side or Server side?

[RettaB]

I am new to web development and am making an app that basically displays a listbox of documents. When the user clicks a document, that document (pdf) is displayed in an iFrame. All the documents are on a network share available from the server and client. This is only going to be used internally (intranet).My questions are:Should I be changing the iFrame source at the server or client? Is it even possible to do it at the client?I am trying to do it at the server. I have the listbox set to auto postback, but I can't read the selectedindex because the page load occurs first (and reloads the listbox) and clears the selected item. If I turn auto postback for the lsitbox off, the SelectedIndexchange event never fires.