What is the safest way to scan documents and an iCloud email account to check if there are any viruses or unauthorised person accessing it?

Garneed wrote:

My documents could have been compromised on a old Mac Air operating High Sierra 10.13.6.

i feel my iCloud email accounts was compromised and the cause of this all. I now want to transfer these documents via an external hard drive. Do you know the safest third party app or program to use to scan these documents and my whole email?

I want everything scanned before I put them into another Mac device.

Please read this excellent user tip:

Effective defenses against malware and ot… - Apple Community