I have a memory stream that contains a PDF file.
Is it possible to view the PDF without saving it to the hard disk ? Process.Start() only takes a path and not a str
Sure, this is certainly possible. Just not via Process Start and Adobe Reader (I assume you are invoking Adobe or something similar)
If you are using .NET or Java you simply need to find a PDF viewer component, there are lots to choose from, google will give you plenty of links, Gnostice has a good one, but its expensive. Once you find a suitable control, view the PDF directly from your app.