To share a document with your colleagues, but only allow them to edit certain portions of it, you can use the Restrict Editing tool on the Review tab, Protect group.
To begin, click the Restrict Editing button, and in the panel that pops up on the right, click the box under Editing Restrictions. Leave the “No changes” default, and select the parts of the document that you want to leave editable by others. After each selection, click the checkbox to the left of “Everyone” under Exceptions. Click the “Yes, Start Enforcing Protection” button and save the document.