public void ExtractText()
{
    //Initialize the SDK library
    //You have to call this function before you can call any PDF processing functions.
    PdfCommon.Initialize();

    //Open and load a PDF document from a file.
    using (var doc = PdfDocument.Load(@"c:\test001.pdf"))
    {
        foreach (var page in doc.Pages)
        {
            //Gets number of characters in a page or -1 for error.
            //Generated characters, like additional space characters, new line characters, are also counted.
            int totalCharCount = page.Text.CountChars;

            //Extract text from page to the string
            string text = page.Text.GetText(0, totalCharCount);

            page.Dispose();
        }
    }

    //Release all resources allocated by the SDK library
    PdfCommon.Release();
}