DPI controls raster dimensions
PDF coordinates are based on 72 points per inch. Rendering at 144 DPI approximately doubles each page dimension compared with 72 DPI, creating about four times as many pixels. This is why 300 DPI can consume far more memory than 150 DPI.
Choose 120–150 DPI for screen review, 200 DPI for clearer details and 300 DPI only when the output purpose and available memory justify it.
JPG or PNG
JPG is usually smaller for scanned or photographic pages. PNG preserves sharp flat-color edges and avoids lossy artifacts but can be much larger. The source PDF may contain vectors, yet any exported page image is rasterized at the chosen DPI.
Process a deliberate range
Use ranges such as 1-10,15,20-25. Exporting sequentially limits peak canvas memory, but the ZIP and PDF buffers still consume space. For hundreds of pages, work in batches and verify the first output before committing to a long run.