4.2.3 Control of documents : Documents required by the quality management system shall be controlled. Records are a special type of document and shall be controlled according to the requirements given in the control of records. Documents shall be approved, signed and dated by the appropriate and the authorised person. A documented procedure shall be established to define the controls needed— (a) to review and approve documents for adequacy prior to issue; (b) to review and update as necessary and re-approve documents; (c) to ensure that changes and the current revision status of documents are identified; (d) to ensure that relevant versions of applicable documents are available at points of use; (e) to ensure that documents remain legible and readily identifiable; (f) to ensure that documents of external origin are identified and their distribution controlled; and (g) to prevent the unintended use of obsolete documents, and to apply suitable identification to them if they are retained for any purpose. Changes to document shall be reviewed and approved. Change records shall be maintained which will include a description of the change, identification of the affected documents, the signature of the approving individual, the approval date, and when the change becomes effective.