https://thenextweb.com/tech/2019/04/09/slack-now-lets-you-preview-documents-within-the-app-and-plays-nice-with-office-365/

It’s a big day for Slack. Today, the enterprise messaging app ticked off an item that’s long been top of users’ wishlists and announced new integrations with Office 365. Let’s start with the former first, as (speaking personally) it’s the most exciting.

Essentially, Slack now lets you preview documents within the app, thereby removing the need to open them externally. From today, if someone drops a Word, Powerpoint, or Excel document in a chat window, Slack will render the first page. Clicking on it will allow you to scroll through the document without having to download it to your device.