We are going to need more information in order to help you.
First: Adobe is a company, so what exactly are you trying to download? Is it Lightroom? There are multiple versions of Lightroom (CC and Classic). Please describe exactly what you are trying to download. You’ve posted in the forum for Lightroom CC for mobile and AppleTV, but we can move the post if needed to another forum.
Second: Please tell us about your device and operating system. Do you have an iPhone? Apple TV? Laptop? Windows or Mac? What version?
When you say “it appears on the screen but when I try to open it - it said it doesn’t exist” can you provide more of an explanation of what it is that appears, what you are doing to open it, and maybe provide a screen snapshot of the error message?
I know that’s a lot of questions, but we need as much information as possible to be able to help get you going.