Mac won't open the file. saying malware or developer not identified.

You might be seeing a message like "Realbooks Software 5.02m.pkg cannot be opened because it is from an unidentified developer. Mac OS cannot verify that this app is free from malware."

Mac operating system's default security settings can block the installation of apps that were not purchased through Apple's app store. 

We do not sell through the Apple store.

That is a harshly discriminating and despicable practice, but they do it anyway.

You'll have to change your setting in order to allow the installation to take place

Beginning with macOS Mojave, when an app fails to install because it "hasn’t been notarized" or "is from an unidentified developer", it will appear in System Preferences > Security & Privacy, under the General tab.

Click Open Anyway to confirm your intent to open or install the app.

The warning prompt reappears, and you can click Open.*

The app is now saved as an exception to your security settings, and you can open it in the future by double-clicking it, just as you can any authorized app.

Our software is 100% safe. You have no worries from the fear inspiring warning from Apple.

We couldn't stay in business long if we included malware or other natsties in our software, could we?!?!

If that still hasn't addressed the issue, check out this article on the web.

Here is a link for reference.

https://macpaw.com/how-to/fix-macos-cannot-verify-that-app-is-free-from-malware#:~:text=From%20Malware%E2%80%9D%20error%3F-,The%20%E2%80%9CmacOS%20cannot%20verify%20that%20this%20app%20is%20free%20from,signature%20is%20corrupted%20or%20invalid.