Copy Text from Large PDF File

Open that PDF in Preview with thumbnails. Click on the page numbered thumbnail, and select/copy that particular page content and then paste it within the Pages document. The assumption here is that the PDF does not have user restrictions on copying content from it.

Alternatively, if you have access to MS Word 16.31 or later for Mac, you can open the PDF and convert it to Word's Docx format. That can be opened in a separate Pages window, and copy/paste from the respective pages into another open Pages window is possible.

The best way to do it is going to depend on how the document was created in the first place. Some pdfs are essentially pictures of documents and it's hard to select and copy text. Others will let you do it just as if you were copying from any place else.

I use the full version of Acrobat and it lets me export PDFs to Word format (which, I believe, can be opened in Pages). The results of the export can be a bit interesting. However, the problems are usually more with complex formatting than with text itself.