主题：读取pdf

Dim reader As New iTextSharp.text.pdf.PdfReader("d:\test.pdf")

Dim n As Integer = reader.NumberOfPages
Dim str As String = ""
For i As Integer = 1 To n
    Dim strategy As object = New iTextSharp.text.pdf.parser.SimpleTextExtractionStrategy()
    Dim currentText As String = iTextSharp.text.pdf.parser.PdfTextExtractor.GetTextFromPage(Reader, i, strategy) 

messagebox.show(currenttext)   
    currentText = Encoding.UTF8.GetString(ASCIIEncoding.Convert(Encoding.[Default], Encoding.UTF8, Encoding.[Default].GetBytes(currentText)))

messagebox.show(currenttext)   
    str &= currentText    
Next
msgbox(str)
reader.Close()

messagebox.show()显示啥也没有，不知道为什么？