Is there a way, using XFile's object model, to detect which version is installed on the client machine?

There is an undocumented Version property on the XFRequest object which will return the version number of saxfile.dll. There is no Version property for the visual control (the AXFFile object) so make sure to get a handle on the XFRequest object.

Examples:

Client-side VBScript:

<script Language="VBScript">
'--- This assumes XFile is already installed on the client.
'--- Otherwise the object should be instantiated using an OBJECT tag
dim XFile = CreateObject("SoftArtisans.XFRequest")
msgBox(XFile.Version)
</script>

<script type="text/javascript">
// This assumes XFile is already installed on the client.
// Otherwise the object should be instantiated using an OBJECT tag
var xfile;
xfile = new ActiveXObject("SoftArtisans.XFRequest");
alert(xfile.Version);
</script>

BSTR bstrVersion; 
HRESULT hr; 
hr = pXFRequest->get_Version(&bstrVersion);