Only the person sharing the encrypted file needs the premium version – the recipient(s) can quite happily use the free version to decrypt/view the file.
When you’re talking about their “online store” I’m assuming you’re referring to the cloud (e.g. Google Drive, Dropbox, OneDrive)? If so then as long as both users have access to either the same cloud account or shared folder (you do this via the cloud app not AxCrypt) then any files contained in that shared folder (whether encrypted or not) can be opened by each party.
For example if I shared a Google Drive folder with you then you’d be able to see the contents – e.g. some work-related photos etc. I could put some confidential documents in the same folder but for added security (because Google Drive isn’t encrypted) I’d encrypt them with AxCrypt and then share the file with you via AxCrypt. You’d already have access to the shared folder. There might be some files in that folder that I don’t want you to have access to … thus I wouldn’t share those with you via AxCrypt even though Google Drive would show you that the file was there.
Does that make sense?
In terms of sharing keys you don’t need to worry about that as AxCrypt handles everything behind the scenes.
To make it clear – AxCrypt is not a cloud service but Google Drive, Dropbox etc. are. Therefore AxCrypt is used to encrypt files in otherwise insecure online cloud repositories.
All you do is share a file through AxCrypt and then either upload the file it into the cloud, send it via email or burn it to a DVD.