In case you have the right to moderate a certain forum, then you can hide posts and comments, and if the owner of the forum has set it, then the moderators of the forum can modify and delete the comments, and delete attachments from comments. 

These options can be found after moving the cursor over the selected comment or post, on the right side, and the appearing 'X' on the right side of the attached document. 

Hidden comments are visible for users with moderating right, and they can be restored with the 'Restore' button.