The abstract of the paper should be concise. The abstract of the paper should mainly explain the purpose, method, result and theory of the paper concisely, and the background purpose can be summarized in a simple sentence or two. So you can't quote others in the abstract of the paper.

The introduction can explain the research background in detail, so you can describe and quote others in the introduction.

You can quote, but try to quote as little as possible.

It is no problem to quote others' words in the abstract, but the abstract itself is only about 200 to 300 words, so even if you drink as little as possible, you can't quote too many abstracts. After all, this means that if you quote others too much, you will deviate from the main point.

The abstract of a paper is generally an introduction to the research background of the paper, and rarely quotes other people's words in the abstract.