Thank you for your reply. However, I do NOT name the file, and this really is what I need help with. The file is opened via a browser URL such as follows:
/dev50-cgi/cfxsof?4F66505C2F6B574F713225584D513E585B4F4F506E4 97E79704C55214E38515657564B7B77543C5A723D3E2658686 72B265A7932

... where cfxsof.exe is a CGI program which takes a single encrypted string referring to a file to display in the browser (either an Adobe PDF or an Excel). cfxsof then writes the contents of this file to the output stream and hence this is handled by the browser. The first line of this file has the following:
Content-type: application/vnd.ms-excel

However, the browser creates a temporary filename in its cache typically named cfxsof.xls, or cfxsof, as in the message:


My question is now: how do I influence the name of the temporary file so that it is compatible with the contents that Excel discovers? It seems to me that it is this temporary file name created by the browser which is the crux of the problem.
Thanks in advance.