在VB.NET中将进程分配给word.application变量

Question

我正在自动执行一个Word文档，该文档在每次单击网页中的一个按钮时都会生成，我可以控制WINWORD.EXE进程，但无法将其设置为word类型变量。 这是我尝试过的：

    Dim ProgID As String = "Word.Application"
    Dim app as Word.Application
    Dim doc as Word.Document
    Dim p() As Process = Process.GetProcessesByName("WINWORD")
    For Each itm As Process In p
        If InStr(itm.MainWindowTitle, LetterType) > 0 Or 
            itm.MainWindowTitle = "" Then
            Dim retVal As Object = Marshal.GetActiveObject(ProgID)
            Try
                app = Marshal.GetActiveObject(ProgID)
                doc = app.ActiveDocument
            Catch ex As Exception
                MsgBox(ex.Message)
        End Try
        End If
    Next

将reVal设为对象= Marshal.GetActiveObject（ProgID）会引发错误：

System.Runtime.InteropServices.COMException：'操作不可用（HRESULT的异常：0x800401E3（MK_E_UNAVAILABLE））'