The PdfTextDocument class is the base class for extracting searchable text from an existing pdf file. Below is a method showing how to extract an entire page of text from the pdf file:

C#

using (PdfTextDocument doc = new PdfTextDocument(docpath))
{
    PdfTextPage page = doc.GetPage(0);
    string s = page.GetText(0, page.CharCount);
    MessageBox.Show(s);
}

VB.NET

Using doc As New PdfTextDocument(docpath)
    Dim page As PdfTextPage = doc.GetPage(0)
    Dim s As String = page.GetText(0, page.CharCount)
    MessageBox.Show(s)
End Using

Original Article:
Q10291 - HOWTO: Extract Text from a Pdf Document