In my desperate search for ways to optimize PDF files, I’ve found that there aren’t many free options. Although there are a lot of shareware programs, there are also, thankfully, a few free programs can help you reduce a PDF file size.
Irfanview & GhostScript [Windows & Possibly Linux]
If you don’t have Irfanview, you should really consider downloading it. It’s a much better and lightning fast alternative to the default image viewer in Windows, supports countless plugins that allow it to be extremely versatile, and converts images to different file types. You can use it to add borders and watermarks to your photos, and batch process many images at a time. You can also view PDF files, provided you download GhostScript first.