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I am currently looking for a PDF library that my company can use. I have built a simple application that displays a single page PDF on a WinForm and what I have noticed is as I re-size my form the memory usage increments and will eventually run out of memory. Is there some way to clear the memory? I noticed in adobe reader it does the same thing but after the memory gets to a certain range adobe clears it some how and the memory usage drops back. Can QuickPDF do the same thing? I am using Windows XP and VB.Net 2010. Following is the code I am using:

Imports System.Runtime.InteropServices Imports QuickPDFAX0726

Public Class Form1

Private Enum SizeEnum

FitToWidth
FitToHeight
FitToPage
ZoomIn

End Enum

Private _currentSizeMode As SizeEnum

Private _rendering As Boolean
Private _qp As PDFLibrary
Private _fh As Integer
Private _ph As Integer
Private _pages As Integer
Private _curPage As Integer

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) 
   Handles MyBase.Load

_qp = New PDFLibrary
_qp.UnlockKey("<put your license key here>")

If IO.File.Exists("C:\Temp\13724601.pdf") = False Then

MessageBox.Show("File does not exist")
Exit Sub

End If

_fh = _qp.DAOpenFile("C:\Temp\13724601.pdf", "")
_pages = _qp.DAGetPageCount(_fh)
_curPage = 1
_ph = GetPage(_fh, _curPage)

DisplayPage(SizeEnum.FitToPage)

End Sub

Private Sub Form1_FormClosed(ByVal sender As Object, 
 ByVal e As 
 System.Windows.Forms.FormClosedEventArgs) 
 Handles Me.FormClosed

On Error Resume Next

_qp.DACloseFile(_fh)
_qp = Nothing

End Sub

Private Function GetPage(ByVal daFileHandle As Integer, ByVal pageIndex As Integer) 
 As Integer

Return _qp.DAFindPage(_fh, pageIndex)

End Function

Private Sub DisplayPage(ByVal sizeMode As SizeEnum)

Dim image As Image = Nothing
Dim renderingDPI As Integer
Dim renderingWidthDPI As Integer
Dim renderingHeightDPI As Integer
Dim widthPoints As Double
Dim heightPoints As Double

Try

If _rendering Then Exit Sub

_rendering = True
_currentSizeMode = sizeMode

widthPoints = _qp.PageWidth
heightPoints = _qp.PageHeight

Select Case sizeMode

Case SizeEnum.FitToPage

renderingWidthDPI = Convert.ToInt32(PictureBox1.Width * 72 / 
widthPoints)
renderingHeightDPI = Convert.ToInt32(PictureBox1.Height * 72 / 
 heightPoints)

If renderingWidthDPI < renderingHeightDPI Then

renderingDPI = renderingWidthDPI

Else

renderingDPI = renderingHeightDPI

End If

image = New Bitmap(Convert.ToInt32(widthPoints * renderingDPI / 72), 
Convert.ToInt32(heightPoints * renderingDPI / 72))

Using graphx = Graphics.FromImage(image)

Dim dc As System.IntPtr = graphx.GetHdc
_qp.DARenderPageToDC(_fh, _ph, renderingDPI, dc.ToInt32)
graphx.ReleaseHdc(dc)

End Using

PictureBox1.Image = image

End Select

_rendering = False

Catch ex As Exception

_rendering = False

End Try

End Sub

Private Sub PictureBox1_SizeChanged(ByVal sender As Object, ByVal e As 
System.EventArgs) Handles PictureBox1.SizeChanged

DisplayPage(_currentSizeMode)

End Sub

End Class

Try calling:

image.Dispose() after PictureBox1.Image = image;