merge pdfs with itextsharp and assign bookmarks

I got this issue from a previous post...

http://www.vbforums.com/showthread.p...sharp+bookmark

This works exactly as I would like it to - it merges pdfs and it sets bookmarks. My issue is that it doesn't release the files. I have to wait until my application closes to access any files again or it says it's in use by another application.

People have mentioned a "Using" command instead but how would I structure this code for "Using"?

Code:

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    Public Function MergePdfFiles(ByVal pdfFiles() As String, ByVal outputPath As String) As Boolean
            Dim result As Boolean = False
            Dim pdfCount As Integer = 0    'total input pdf file count
            Dim f As Integer = 0            'pointer to current input pdf file
            Dim fileName As String = String.Empty  'current input pdf filename
            Dim reader As iTextSharp.text.pdf.PdfReader = Nothing
            Dim pageCount As Integer = 0    'cureent input pdf page count
            Dim pdfDoc As iTextSharp.text.Document = Nothing    'the output pdf document
            Dim writer As PdfWriter = Nothing
            Dim cb As PdfContentByte = Nothing
            'Declare a variable to hold the imported pages
            Dim page As PdfImportedPage = Nothing
            Dim rotation As Integer = 0
            'Declare a font to used for the bookmarks
            Dim bookmarkFont As iTextSharp.text.Font = iTextSharp.text.FontFactory.GetFont(iTextSharp.text.FontFactory.HELVETICA, _
                                                                      12, iTextSharp.text.Font.BOLD, iTextSharp.text.Color.BLUE)
            Try
                pdfCount = pdfFiles.Length
                If pdfCount > 1 Then
                    'Open the 1st pad using PdfReader object
                    fileName = pdfFiles(f)
                    reader = New iTextSharp.text.pdf.PdfReader(fileName)
                    'Get page count
                    pageCount = reader.NumberOfPages
                    'Instantiate an new instance of pdf document and set its margins. This will be the output pdf.
                    'NOTE: bookmarks will be added at the 1st page of very original pdf file using its filename. The location
                    'of this bookmark will be placed at the upper left hand corner of the document. So you'll need to adjust
                    'the margin left and margin top values such that the bookmark won't overlay on the merged pdf page. The
                    'unit used is "points" (72 points = 1 inch), thus in this example, the bookmarks' location is at 1/4 inch from
                    'left and 1/4 inch from top of the page.
                    pdfDoc = New iTextSharp.text.Document(reader.GetPageSizeWithRotation(1), 18, 18, 18, 18)
                    'Instantiate a PdfWriter that listens to the pdf document
                    writer = PdfWriter.GetInstance(pdfDoc, New IO.FileStream(outputPath, IO.FileMode.Create))
                    'Set metadata and open the document
                    With pdfDoc
                        .AddAuthor("Your name here")
                        .AddCreationDate()
                        .AddCreator("Your program name here")
                        .AddSubject("Whatever subject you want to give it")
                        'Use the filename as the title... You can give it any title of course.
                        .AddTitle(IO.Path.GetFileNameWithoutExtension(outputPath))
                        'Add keywords, whatever keywords you want to attach to it
                        .AddKeywords("Report, Merged PDF, " & IO.Path.GetFileName(outputPath))
                        .Open()
                    End With
                    'Instantiate a PdfContentByte object
                    cb = writer.DirectContent
                    'Now loop thru the input pdfs
                    While f < pdfCount
                        'Declare a page counter variable
                        Dim i As Integer = 0
                        'Loop thru the current input pdf's pages starting at page 1
                        While i < pageCount
                            i += 1
                            'Get the input page size
                            pdfDoc.SetPageSize(reader.GetPageSizeWithRotation(i))
                            'Create a new page on the output document
                            pdfDoc.NewPage()
                            'If it is the 1st page, we add bookmarks to the page
                            If i = 1 Then
                                'First create a paragraph using the filename as the heading
                                Dim para As New iTextSharp.text.Paragraph(IO.Path.GetFileName(fileName).ToUpper(), bookmarkFont)
                                'Then create a chapter from the above paragraph
                                Dim chpter As New iTextSharp.text.Chapter(para, f + 1)
                                'Finally add the chapter to the document
                                pdfDoc.Add(chpter)
                            End If
                            'Now we get the imported page
                            page = writer.GetImportedPage(reader, i)
                            'Read the imported page's rotation
                            rotation = reader.GetPageRotation(i)
                            'Then add the imported page to the PdfContentByte object as a template based on the page's rotation
                            If rotation = 90 Then
                                cb.AddTemplate(page, 0, -1.0F, 1.0F, 0, 0, reader.GetPageSizeWithRotation(i).Height)
                            ElseIf rotation = 270 Then
                                cb.AddTemplate(page, 0, 1.0F, -1.0F, 0, reader.GetPageSizeWithRotation(i).Width + 60, -30)
                            Else
                                cb.AddTemplate(page, 1.0F, 0, 0, 1.0F, 0, 0)
                            End If
                        End While
                        'Increment f and read the next input pdf file
                        f += 1
                        If f < pdfCount Then
                            fileName = pdfFiles(f)
                            reader = New iTextSharp.text.pdf.PdfReader(fileName)
                            pageCount = reader.NumberOfPages
                        End If
                    End While
                    'When all done, we close the documwent so that the pdfwriter object can write it to the output file
                    pdfDoc.Close()
                    result = True
                End If
            Catch ex As Exception
                Throw New Exception(ex.Message)
            End Try   
            Return result
        End Function

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