Do I need an antivirus?

I'm quite new to Linux and I've seen several videos on YouTube saying that you don't need an antivirus for Linux. However, I often download files from the Internet (mainly PDFs) and I'm not always sure whether these websites are trustworthy and whether these files are safe. Should I download an antivirus? Are there any other precautions that I should take to ensure I don't install malware? (I use Linux Mint OS Cinnamon and have GUFW set up).