The Uncensored Man by Arthur Sellings: copyright 1964 in Britain / the (only) American edition was a 1967 paperback.

Dr. Mark Anders was one of the government's top physicist, working on a high-priority project concerning defense. He began to receive messages in strange form: the babblings of an epileptic, the output sheet of a new super-computer… This was only the beginning, for he was soon transported to a different dimension, whose people had been desperately trying to contact him to deliver a message terrifying in its implications for the future of the human race…