Concern that Adobe Inc. will struggle in the artificial-intelligence era has driven Wall Street analysts’ view on the maker of software for creative professionals to its most pessimistic in more than a dozen years. Oppenheimer cut its assessment of the stock to perform on Tuesday, the latest in a series of downgrades as analysts fret the company’s growth outlook will be weaker in the face of competition from companies including OpenAI, which allow users to generate images and videos from prompts...