Master documents are read-only except when a new revision is released from a project folder. Therefore, all changes must be made to a project copy of the master document that resides in a project folder. What's more, changes can only be made to the project copy while it is in workflow. This process is known as Change management.
The whole process of changing a master document includes:
Make a project copy of the master document as described in Project Copies.
Start the document in a workflow as described in Document workflow and Run a workflow transition.
When the document is in the Under Change state, change it as necessary as described in Open a document from within Meridian.
Route the document completely through the workflow as described in Run a workflow transition until it is in the Issued or Released state depending on its document type.
Release the changes as a new revision of the master document as described in Release a project copy as a new master document.