PDF files used to open in Preview but Adobe reader has taken over. How can I return to Preview being the only application opening PDF files when I download or save them?

When viewing and downloading PDF files from Safari they used to open in Preview either in the preview application or an online version where you can open or save in preview format. But now Adobe reader has taken over so that whenever I open a PDF file on Safari and try to save it makes me save it as an Adobe Reader file and I can't change it to Preview. I don't know why this has started happeing because I've not changed any settings to make Adobe the primary application. How can I return to Preview being the only application opening PDF files when I download or save them?

Please help if you can.

Thanks.