This is a four-character fixed expression (固定短语) meaning 'unbearable' or 'hard to endure'. It is used in both spoken and written Chinese, but carries a slightly formal or emphatic tone — stronger than 受不了 (which is more colloquial). You can use it to describe physical pain, emotional distress, or intolerable situations. The structure is fixed: 难以 (hard to) + 忍受 (endure).