0 to understand something (from a piece of writing etc) which is not actually stated -- ทำความเข้าใจความหมายที่แฝงไว้
1 to look for or find information (eg in a letter) which is not actually stated -- อ่านเพื่อจับความหมายแฝง
Reading between the lines I get the impression that he wants to leave the company.