"Cost" in the last sentence can be replaced with "expense", "price", or "costs". That's straightforward.
Serial -> Serial
Now, looking at the provided text. The first sentence is: "Buy a valid license from Adobe or an authorized reseller." Here, Adobe is a proper noun, so I shouldn't change that. The other words like "Buy," "valid," "license," "authorized," "reseller" need to be converted. For each, I need to come up with three synonyms or similar words. Let me start with "Buy": maybe "Purchase," "Obtain," "Acquire." "Valid" could be "Legit," "Genuine," "Authentic." "License" might stay as "License," but maybe "License Key," "Software Authorization," "Permit." Wait, but the instruction says every word with three variants. Hmm, maybe I need to adjust "License" to have three different terms, but some might not have direct synonyms. I'll have to think creatively. Adobe Photoshop Cc 2015 Serial Number Generator
Let me check the first sentence: "By understanding the benefits and risks of using an Adobe Photoshop CC 2015 Serial Number Generator, you can make an informed decision about how to access this powerful image editing software." "Cost" in the last sentence can be replaced
Number -> Number