I want to promote an eBook with lots of affiliate links in it - trouble is I don't want people to start changing the affiliate links to their own when they start sharing it. How can I prevent the links from being tampered?
First, if it's a free ebook, it's okay to put affiliate links in it. But I wouldn't recommend loading up an ebook that you plan to sell with affiliate links. You will most likely never get those customers to buy your next product.
As far as protecting affliliate links in an ebook, even if you use the option in your PDF creation app (Adobe Acrobat, or Nitro PDF, or Foxit, etc.) to protect it from being edited, there are programs that can easily break that protection. Then it can be edited to enable them to put their affiliiate links in it.
So ultimately, there is no way that you can prevent it from being tampered with.