Each chat room, no matter private or a group room, has the "Send File" button in the toolbar just above the message input field.
Besides using this button, you can also copy and paste any file into the chat room. You can either right-click in the message input field and select "Paste" to paste the file which you previously copied, or you can use the Ctrl+V (Command+V for Mac) shortcut to paste the file.
There is also another way to send a file - simply by dragging and dropping it into the chat room.
You can choose the method you are most familiar and comfortable with or use them interchangeably.
All files transferred in the chat rooms are stored timelessly, so you can access and download them at any time.
You can either send files as separate messages or attach them to existing ones. Just drag the file to the message you need and drop it there. The other way is to right click the message and choose “Attach file” option.
To save a file locally, click the paperclip icon on the left of the file title, choose the location on your computer where you want to save the file, and click "Save".
Alternatively, you can click the "More Options" icon, which is located to the right of the file title, or just right-click on the file title and select "Download attachment".
If you would like to delete a file from the conversation, similarly, open the "More Options" menu and select "Delete attachment".