Please check the number of application in taskbar and the consumption of ram and memory, generally if you put pressure on ram it will heat-up the laptop.

It is showing white pdf file because of 2 reasons. (1) It is corrupted so need to repair the PDF document (2) It is too heavy in size and thus not supported by your pdf viewer software, you can reduce the size using compress pdf tool. (3) PDF file is blank from the start so it is showing white background.