Solution how to import contents of a .txt file into a body field? Are any solution how we can import content of text (.txt) file with feeds into body field?

We don't have any problem with standard feeds import with CSV file and files into field file. We just need solution how we can import content of separate text file into body field.

Thanks
I believe you can accomplish this with Feeds Tamper and a custom plugin.

Take one of the existing text plugins and clone it to a new one.  Then inside the plugin callback, take the cell value (your text file name), build up a proper path, do a file_get_contents(), and stuff the contents into the result.

If you end up going this route, it may be a decent patch to Feeds Tamper for inclusion in the project itself.