Often we get files via emails and other means which could contain viruses. Its a good idea to ignore such emails. An example, innovative one I received had a Google drive attachment.
The drive had a "nice" pdf with a clickable link.
(The green button is a clickable link)
How do we identify whether the file has a virus ?
First and foremost avoid downloading such suspicious or lucrative files. Even if there is an anti-virus, this may not get identified.
Personally I tend to save them safely and upload to VirusTotal.com for inspection. This acts a means for community to get alerts about suspicious new attack vectors.
(https://www.virustotal.com file upload interface)
Once the file is uploaded, different antivirus engines performs testing in real time.
Its interesting to note that only one AV engine has identified the malware. This also shows that downloading files even without active anti-viruses could be a potential risk.