From the Knowledgebase

PDF files are slow and how to optimize a PDF file to render it faster?

Typically, PDFs with a smaller file size will be rendered faster and it depends on how big a single page is. The amount of pages does not affect the performance because we are loading and rendering only those pages that are currently visible.

You must optimize your documents for the web for better and faster results. See Optimize a PDF from Adobe's website for more information.

There are more improvement techniques that we can suggest:

  1. Avoid using high-resolution images - 150 dpi resolution for scanned images should be more than enough for screens, especially for low-powered devices (phones).
  2. Try to use JPEG encoding for color images/photos in RGB colorspace when possible.
  3. Avoid using expensive compositions/effects such as transitions or masking - flatten the transparency.
  4. Avoid using PDF generators (or don't create content) that produce ineffective PDF output (e.g. LibreOffice creates a lot of tiny images for vector elements/pictures it does not understand).
  5. If there is such a setting, use web-optimized PDF output or use linearization.
  6. Fix or don't produce corrupted PDFs that do not conform to the PDF32000 specification.