i already used another text box that shows the path of the file, and i used a validator to check if it's empty or doesn't contain a file:

function validateFile(source, args) {

var regex = /.*\..{3,4}/;

var textBoxFileName = document.getElementById('<%=TextBoxFileName.ClientID%>');

if (textBoxExistingFile != null && textBoxFileName != null)

{

if (textBoxFileName.value.length == 0 ||

textBoxFileName.value.search(regex) == -1)

{

args.IsValid =

false;

return;

}

}

args.isValid =

true;

}

function fillFileName(sender, args) {

var label = document.getElementById('<%=TextBoxFileName.ClientID%>');

if (label != null)

label.innerText = args.get_item().get_path();

OnClientItemSelected(sender, args);

}

<telerik:RadFileExplorer ID="RadFileExplorer1" runat="server" Configuration-MaxUploadFileSize="307200"

EnableCreateNewFolder="false" EnableOpenFile="true" OnClientItemSelected="fillFileName">

<Configuration SearchPatterns="*.jpg,*.jpeg,*.JPG,*.JPEG,*.gif,*.GIF,*.png,*.PNG" />

</telerik:RadFileExplorer>