Hi, I have question about Pages and licence.

This is an example:

I have my community installed on subdomain invision.domain.tld

There are forums, gallery, blog etc.

And now via Pages I want to create landing pages for my community, which would be located in root (domain.tld)

Is it possible by Pages and it's allowed by licence which is valid for subdomain?

This is not something in which is possible on the platform at present time. The license is unable to be used over more than one subdomain, in terms of both software and indeed licensing. 

Well, you could think in the future about the option that if I have a community on a subdomain, could it somehow be possible to extend the pages to the main domain, perhaps as part of some paid application. ( low fee 😀 )

The software is actually built to be used on the main domain. If you are using pages as the main part of your site, you would then set pages as the default application so you have as follows

blah.com/ - Pages page
blah.com/forums
blah.com/events

etc

I am admin of three invision sites. Two are on subdomain, one is on root. All run good :)