To make our downloads simpler and quicker we often combine pdf files into a single downloadable Zip file. Normally your standard native application on your PC or Mac will be able to extract the downloaded zip file without any issues. Sometimes though, usually due to file name limitations in Windows you need a slightly more advance app to extract your zip file.
We recommend using 7Zip. This is a free app that has been an industry standard for many years, and tends to handle all zip extractions with ease. Here is a link to download it:
If you are still having issues you should raise a support ticket from our homepage or your account dashboard and we will do our best to help you.