Thank you for reaching out.
Please let us know if you are trying to copy text from PDF and pasting on some other file.
If yes, ensure that you use the "Selection tool" to select the text in the PDF. When you select the text, you get the pop-up toolbar.
Select Copy text icon, and then you may paste it.
You may also refer to the information provided on the following help page: https://helpx.adobe.com/reader/using/copy-content-pdfs.html.
Let us know if you have any questions.