SAN FRANCISCO — In one of Silicon Valley’s most closely watched cases, a federal judge on Thursday certified a class of more than 60,000 skilled workers who accuse Adobe Systems Inc., Apple Inc., Google Inc. and Intel Corp. of illegally suppressing their pay through a conspiracy not to compete for each other’s employees.

“This court could not identify a case at the class certification stage with the level of documentary evidence plaintiffs have presented,” wrote U.S. District Judge Lucy Koh of the Northern District of California.