Thanks for your answer, and sorry that it took so long for me to reply.
Concerning the ways to add a summary to a page, I know them well and use them regularly. I used an additional editor because it’s not really a summary that I need, but a text I can use independently from the main content. To make it more clear, I’m constructing a blog with multiple articles. On the blog page I want to show the summaries of the main contents, but on the articles’ pages I want to add a “pre-text” before the main content (in french it’s called a “chapô”). And for this chapô I want to have the possibility to use shortcodes, which are currently not functionning.
The markdown syntax is working fine in this chapô’s editor : I can use bold, italic, make links, etc. Only the shortcodes are not working.
I’ve thought that it would may be due to the shortcode’s plugin which only takes the main content into account, but I’ve not been able to find such a specification in the plugin’s files…