By default, the free version of Foxit Reader has five Ads. You can prevent them from appearing again by disabling each of them one by one. To disable the ads, follow the instructions in this tech-recipe.
1. Open up a PDF file in Foxit Reader.
2. You will notice an add in the upper right corner.
3. Click View, and then click Advertisement to turn it off.
4. Close Foxit Reader.
5. Repeat Steps 1-4 until no ads appear in the upper right corner.
By taking just a minute or two to do this, you will never be bothered by these ads again.