One solution is check the files in virus total
Simplifying that:
Download VirusTotal Uploader - Upload files for scanning with the VirusTotal service, either by using drag and drop or from the context menu, with this open-source utility
www.softpedia.com
VirusTotal also offers several client-side tools to help users more seamlessly interact with the VirusTotal service. There are flavors of these tools for the major operating systems, refer to the s...
www.virustotal.com
Because nobody has mentioned it, I will insert that one of the most highly regarded antiransomware programs is WAR, Win Anti-Ransomware, by the same outfit as WinPatrol. It's shareware, but it's not real expensive.
Given your lack of income available to buy software, I would really suggest strongly that you subscribe to some websites that offer temporary giveaways of shareware. I know of three good English language ones. Two are
BitsDuJour and
Giveaway of the Day.
Giveaway Club is not as good as the three I have in mind, but you can get some good stuff there. Backup programs are sometimes offered for free from these giveaway sites.
You may also be able to get a perfectly adequate backup program solution with freeware. Do searches for things like "best free backup programs". There are some websites that specialize in free software, such as
Gizmo's. You can go to the forum there and ask for recommendations., as well as making a thread to ask for recommendations here.
There are also some free cloud storage websites. Search "best free cloud storage / online backup". Obviously the support and service cannot be expected to be as good as with paid, but it's better than nothing. You can compensate for size limits by using more than one. The standard expert advice is backup both to an external hard drive and to the cloud. I also recall a free program called something like Backup Buddy that allows you to back up, encrypted, to a friend's computer.
Keep in mind there are more reasons than just ransomware protection to want to have backups.