It depends upon the DLLs that the default application uses to show the .txt file to the user: the application has to try to install a DLL that is not in the usual places (i.e., system & windows directories and the application directories). So there is likely to be some speculative DLL lookup going on for apparently well-behaving code to be vulnerable to this.
From the description of the vulnerability, it sounds as if the culprit is some code mounting documents over the network, and so just opening a readme.txt in the local directory will not trigger this.
From the description of the vulnerability, it sounds as if the culprit is some code mounting documents over the network, and so just opening a readme.txt in the local directory will not trigger this.