Hi, @Tim Keaty Yes, it is possible to comment on a Trello card from slack; you can do that by adding a comment command. Although, the add Comment command only adds the comment to the last card shown by Trello. But you can add a comment to a different card by pasting the card URL or using the /Trello search to look for the card you want to add a comment to. Below is an example of how to add a comment to a card,
/trello comment [comment text]
Example: /trello comment That’s awesome!
And no, It's not possible to add files such as pdf directly from slack to Trello.
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