How to open a file in Safari without downloading to computer?

[TheRealSweetheart]

I have a MacBook Air and literally every time I click on a file to open it (school/email/Powerpoint slide), it downloads to my computer. Does anyone know how to stop this?? It's really annoying and very unsafe. Back when I had a PC, when I would click on a downloadable link, I would get a pop-up asking me if I wanted to 'open' or 'save' the file. I would click open and it would open in the program and that's it. It never saved to the computer. Please don't tell me to uncheck the box "Open safe files after downloading" in the Preferences tab because that is not my issue. I simply want to open the file in another tab or in the program without it physically saving onto my laptop. This has to be possible.
To Fred, I don't have an anti-virus. And this isn't really primarily a security question. My point is that there should be an option to not automatically download files onto my computer. It's annoying. Secondly, most of the files I download are Microsoft files which are converted into (docX, or PPx) files by Mac. It's not giving me an option as to whether I want it on my computer or not. I want to know how to STOP it from AUTOMATICALLY downloading. Period.

To Aman, I was using Internet Explorer when I had a PC. Next, I'm not only referring to microsoft files. Literally any link I click on in an email such as a flyer, a poster, an invitation to something, obviously powerpoint slides, etc automatically download to my computer.

[Aman Kumar]

Because on "PC" u had a software to open those files instead of directly downloading them and i guess that was Microsoft office and u were using Mozilla Fire fox.

Try to install another browser like mozilla or chrome on ur macbook and see if that works or not .

[Fred]

You can NOT open Microsoft Office files in a browser. Saving a file is safe, it does nothing unless you access the file. Clicking the open button would always have immediately infected the machine if it was a virus or spyware installer. While storing it would allow you to first scan it with your anti-virus first. So your idea of security s wrong.