how can i tell if free software is safe?

[Ben's mum]

I am looking for some free software to have a go at planning our new offices, there seems to be loads of 'free' stuff available with enticing buttons that say 'download now', but I am a bit scared of opening something that has a virus.  Not sure if I am worrying too much as I have windows defender and hopefully that would stop something nasty but after losing one computer to a Trojan thing that wiped the lot I am not so brave anymore!
Are there any ways to tell if something is genuine or safe?

thanks 

[MIN]

go to money saving expert.com. search for Free Antivirus software. scroll down the page to section 5 . there is some info there that might be usefull. i dont know how to send the link  but will pin it incase you can not find it.

[Ben's mum]

Thank you, will have a look now 

[Sheryl]

I have always used Avast or AVG for free x

[PennyB]

make sure you read the small print when you download stuff as while not a virus I innocently downloaded 'iminent' that also took over my browser and no matter how many times I got rid of it it came back - it also kept sending me a popup to download emoticons - all of these are not blocked and impossible to block