The most common delivery method for viruses is through email. Email is responsible for the delivery of about 94% of top malware in the world, of which viruses are part of. Also, the most common medium through which hackers also transfer viruses is through phishing emails.
These hackers carefully craft phishing emails which contain malicious file by causing people to click on a link or open an attachment. Such a file can be seen in different formats, which include zip file, JavaScript, PDF, or word document. The hackers usually trick users into enabling macros in the case of the word document, after the user has opened the document.
This will give permission to the hacker to run a script, which executes a dangerous executable file (EXE) after downloading it from an external web server. When a person can just naively open an attachment present in the phishing email, the whole organization will most likely be infected.