VB.NET Read pdf all context with iTextSharp

Imports iTextSharp.text.pdf

Imports iTextSharp.text.pdf.parser

  Private Function GetPDFContext(filePath As String) As String

        Dim oReader As New PdfReader(filePath)
        Dim pageContextList As New List(Of String)

        For i As Integer = 1 To oReader.NumberOfPages

            Dim its As New SimpleTextExtractionStrategy
            pageContextList.Add(PdfTextExtractor.GetTextFromPage(oReader, i, its))
        Next

        'スペースで各ページの情報を繋ぐ

        Dim allContext As String = String.Join(" ", pageContextList)

        ''エンコードの設定

        'allContext = Encoding.UTF8.GetString(ASCIIEncoding.Convert(Encoding.Default, Encoding.UTF8, Encoding.Default.GetBytes(allContext)))

        oReader.Close()

        Return allContext
    End Function