Usually PDFs are completely fine, but that doesn’t mean they always are. PDFs from unfamiliar websites, suspicious links, or pirated versions of PDFs you normally can’t access (like free books, free documents, or reports) can be riddled with malware just like any other file.
If your device gets infected because of a malicious PDF file, the first thing you should do is avoid contacting the hackers. They may try to steal your data and encourage you to pay them. Then, install good antivirus software (like Norton or Bitdefender) and let it remove the malware from your device.