Working with Comments and Attachments in the Comments Tab
If the proper permissions are granted to you, you can add, delete, modify comments and attachments on a task's Comments tab. At design time, the task developer can set a scope for the comments and attachments, defining how comments and attachments are shared.
Note:
The comment permissions cover functionality for both comments and attachments. That is, if you grant permission to a user for comments, you are also granting permission for attachments.