How can I use vb program to get the text from pdf ?

Here is a function that I can get the page's number of the pdf file.

Public Function GetNumPages(ByVal PdfFile As String) As Long
    Dim objTempDoc As Object
    Dim fso As FileSystemObject
    Set fso = New FileSystemObject
    If fso.FileExists(PdfFile ) Then
        Set objTemp = CreateObject("AcroExch.PDDoc")
        objTemp.Open pstrPdfFilename
        GetNumPages = objTemp.GetNumPages
        objTemp.Close
        Set objTemp = Nothing
    End If
    Set fso = Nothing
End Function

Now I want to get the last line's text in the last page of pdf.

I have no idea to get the text.

Where can I read the technical manual or some document?