[abenedik]

The ReaderWmf internally uses some GDI+ interop methods that take only file name as parameter. Therefore the Read method that takes stream as parameter internally creates a temp file in Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData) folder.

I would advice you to create the temp metafile by yourself in some known location inside your web application and pass use the Read method that takes file name instead of stream.