Every document has a tab called HISTORY which indicates who changed what in that document. An example of this tab for a proposal is shown below.

1. When the document was created and by whom
2. Any fields in your document which were changed. You can see the field name, the old value before the update and the new value after the update. System calculated fields which are changed as a result of a user are included
3. You can see who made each change
4. And when (relative to today)
5. All changes appear by default. You can optionally limit the display to only show changes to attached files and comments, workflow status or field updates. The majority of changes are field updates.