Error when creating pdf with itextsharp

I am trying to write on an existing pdf and get the following error:

System.IO.IOException: The process cannot access the file 'c:\www\vhosts\domain.com\httpdocs\certificates_out\####xxxxx.pdf' because it is being used by another process. at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath) at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs

The weird thing is it still creates it and appears to be working just I keep getting the error.

Any thoughts? I tried having a Using but that didn't work.

Code:

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''' <summary>
    ''' fnCreateCertificate is to create a certificate file and save on the server.
    ''' </summary>
    ''' <returns>saved file and full path</returns>
    ''' <remarks></remarks>
    Public Function fnCreateCertificate() As String
        'determine the full path of target file
        _TargetFullFolderFilePath = _TargetFolderPath & _TargetFilename

        '------ READ and WRITE TO PDF --------
        Dim reader As PdfReader = New PdfReader(_SourcePDFBaseFile)
        Dim n As Integer = reader.NumberOfPages
        Dim psize As iTextSharp.text.Rectangle = reader.GetPageSize(1)
        Dim width As Single = psize.Width
        Dim height As Single = psize.Height
        Dim doc As Document = New Document(psize, 50, 50, 50, 50)

        ''create file stream
        'Dim fsFile As Stream = New FileStream(_TargetFullFolderFilePath, FileMode.Create)

        Try
            'The writer object is responsible for creating the actual PDF file.
            Dim writer As PdfWriter = PdfWriter.GetInstance(doc, New FileStream(_TargetFullFolderFilePath, FileMode.Create))  '<------- THIS IS WHERE THE ERROR IS POINTING TO
            'Dim writer As PdfWriter = PdfWriter.GetInstance(doc, New FileStream(_TargetFullFolderFilePath, FileMode.Create))

            'open document
            doc.Open()

            Dim cb As PdfContentByte = writer.DirectContent

            Dim page1 As PdfImportedPage = writer.GetImportedPage(reader, 1)
            cb.AddTemplate(page1, 0, 0)

            'tell the ContentByte we're ready to draw text
            cb.BeginText()

            Dim bf As BaseFont = BaseFont.CreateFont(BaseFont.TIMES_ROMAN, BaseFont.CP1252, BaseFont.NOT_EMBEDDED)
            Dim bfBold As BaseFont = BaseFont.CreateFont(BaseFont.TIMES_BOLD, BaseFont.CP1252, BaseFont.NOT_EMBEDDED)

            cb.SetFontAndSize(bfBold, 18)
            'draw some text on a certain position
            cb.ShowTextAligned(PdfContentByte.ALIGN_CENTER, _NameOnCertificate, psize.GetRight(0) / 2, _iYPos, 0)
            cb.ShowTextAligned(PdfContentByte.ALIGN_CENTER, _CertificateDateScore, psize.GetRight(0) / 2, 282, 0)

            'tell the contentByte, we've finished drawing text
            cb.EndText()

            'fsFile.Dispose()
        Catch de As Exception
            Dim oSE As clsSendEmail = New clsSendEmail
            oSE.FormSendEmail(System.Configuration.ConfigurationManager.AppSettings("EMAIL-ADMIN"), "The following error occured: " & de.ToString, "Error")
        Finally
            'close the document
            doc.Close()
            'fsFile.Dispose()
        End Try

        Return _TargetFullFolderFilePath

    End Function

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