Loop through Multiple Processes Async

Hello

I have a Program that needs to Generate pdf files (Invoices) for emailing.
I can have up to 50 pdf files to Generate per Email.
I want to loop through all the Files and Generate 5 Async until all files are generated.
i.e. I want 5 pdf files being generated continually until all the files have been generated. (As soon as one finishes I want another one to start - Keeping 5 Being generated)

How do I do this?

Currently I have the Below.

Dim fileList As New List(Of String)

        ' Code to Populate List

        For Each item In fileList
            'Generate PDF of Order
            Dim processToStart As New ProcessStartInfo
            processToStart.FileName = "C:\PDFProgram.exe"
            processToStart.Arguments = item
            processToStart.UseShellExecute = False
            Process.Start(processToStart).WaitForExit()
        Next

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