w3wp.exe and memory with BinaryWrite on windows xp 64bit?

Hello..
My code reading a page from pdf file by PDFLib and sending it to client after putting watermark on the image..
The problem is w3wp.exe posses is eating more memory in every request, so after using the program times the memory will be full.
My Server system is windows xp 64bit.
This is me code:
Public Partial Class readpdf Inherits System.Web.UI.Page Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load Dim FileID As String = Request.QueryString("fileid") If CheckMyVal(FileID, TypeCode.String) = False Then Exit Sub Dim PageN As String = Request.QueryString("pagen") If CheckMyVal(PageN, TypeCode.Int32) = False Then Exit Sub If PDFMainLib.LibIsOpeningNow = False Then PDFMainLib.MyPublicConnectionString = GetConnectionString(True) If PDFMainLib.OpenMyLib(&quo ...