如何为内生性编写正确的代码-R中的面板数据的Hausman测试？

Question

我的代码：

    Public Shared Sub UnhideText(ByVal strFileName As String)
    Dim pdf As iTextSharp.text.pdf.PdfReader = New iTextSharp.text.pdf.PdfReader(strFileName)
    Dim stp As iTextSharp.text.pdf.PdfStamper = New iTextSharp.text.pdf.PdfStamper(pdf, New IO.FileStream("e:\out.pdf", IO.FileMode.Create))

    'This does not work, text remains unvisible. I guess SetTextRenderingMode applies only for new added text.
    For pageNumber As Integer = 1 To pdf.NumberOfPages
        Dim cb As iTextSharp.text.pdf.PdfContentByte = stp.GetOverContent(pageNumber)
        cb.SetTextRenderingMode(iTextSharp.text.pdf.PdfContentByte.TEXT_RENDER_MODE_FILL)
    Next

    stp.Close()
End Sub

而且我总是遇到以下错误：

  

pFtest（FE，OL）中的错误：找不到对象'FE'