Authors often download Acrobat/PDF files when researching a particular topic, then experience issues in bringing that text into their word processor. Copy and paste is of limited utility, and loses local text formatting such as underlines, bolding, italics and superscripting. Fortunately Adobe (the creators of Acrobat) maintain a free online conversion utility: https://www.adobe.com/au/acrobat/online/pdf-to-word.html
A list of other conversion utilities is maintained at the base of that page.