Add cover for a file

If you want to add a cover for the file instead of the default view:

it was, for example, like this:

To do this, in a post with the type "Document", you need to upload the file that will be attached to the post, and click on the paperclip:

In the appeared window you need to select a picture that will be used as a cover:

The result can be checked through the preview in the bot.