Are you converting documents to outlook or outlook items to other formats? You can try using a program like Nitro PDF to accomplish some conversions. Also there are a lot of online converters you can use.
What file extension are you converting from and to?
Yes, there's no need for installing only Microsoft Outlook on your device. The problem of different email formats for various email clients is really widespread, that's why a great amount of alternative software appeared as a solution for this. The easiest way is to use one of online email converters. For example as the best and safest one among them is considered according to many reviews Convert Mail Online convertemail.online/start-the-conversion/ . In order to migrate to Outlook you'll need only several minutes with using it.
I can suggest using the Email Detail Archive. This is a simple future-proof archiving solution - make PDF copies of your emails. You always know how to open a PDF. It's crucial as other archiving providers create custom files that you won't be able to open without additional software. I save emails as PDF files on my hard drive and find it to be very convenient.