I am currently a referee for a paper. One of the authors of the paper had written an earlier paper, which I will refer to as the "original paper," and the paper which I am now refereeing is an extension of the original paper, which I will refer to as the "extension paper."
I have found that large portions of the extension paper are copied from his original paper. In particular, a whole section of definitions is copied from his original paper; and some paragraphs in the introduction and literature review are copied wholesale or with slight modifications from the original paper.
Is it acceptable for an academic paper to copy paragraphs and even a section from an earlier paper by the same author?
My intuition suggests that it is acceptable to copy the definition section, with an acknowledgement that it came from the original paper, since definitions are standard. But it seems strange to me for the introduction and literature review to be too similar to the original paper.