Typically, PDFs with a smaller file size will be rendered faster and it depends on how big a single page is. The number of pages does not affect performance. It's essential that you optimize your documents for the web. See Optimize a PDF from Adobe's website for more information. There are more improvement techniques that we can suggest:
- Save the file as Optimized PDF. In Adobe Acrobat, choose File > Save As Other > Optimized PDF. Instructions >>
- Avoid using high-resolution images -- 150 dpi resolution for scanned images shall be enough for screens, especially for low powered devices;
- Try to use JPEG encoding for color images/photos in RGB colorspace when possible;
- Avoid using expensive compositions/effects such as transitions/masking -- flatten transparency;
- Avoid using PDF generators (or don't create content) that produce ineffective PDF output (e.g. LibreOffice creates lots of tiny images for vector elements/pictures it does not understand);
- If there is such a setting, use web-optimized PDF output/linearization;
- Fix or don't produce corrupted PDFs that do not conform to the PDF32000 specification.