PDF Converter HD Search is a search hijacker and uses web push notifications. Malwarebytes can detect and remove this potentially unwanted program. It would have blocked their website, giving you a chance to stop before it became too late. If you have allowed the notifications you can read here how to disable them. The full version of Malwarebyte would have protected you against the hijacker. The only thing you need to do to get rid of them is to remove them from your computer.”]
Source: https://forums.malwarebytes.com/topic/252534-removal-instructions-for-pdf-converter-hd-search/