PDFDraw needs lots of memory to render/rasterize the page content. The memory requrements depends on the required resoultion. For example 8.5 x 11 inch page at 200 DPI will require 8.5 x 11 x 200 x 72 x 4 bytes … just to store the output image! Once this memoy is allocated it is being reused for subsequent pages. If you want to lower memory requirements please this post…
https://groups.google.com/d/topic/pdfnet-sdk/_vjcnNl-e20/discussion