For your consideration are 2 documents (rare pieces of Britiish history)

1- MILITARY DOCUMENT : GRANT OF THE DIGNITY signed by King Edward VIII Signed as Grand Master Prince Wales Windsor  “Edward P,” dated 3 June 1919.  document measures approximately 12.75" × 15.25" when opened up.  It has a raised seal.  In this Document  King George V appoints John Howard Slayter to temporary Captain of the Medical corps of the forces of our dominion of Canada

NOT SURE if Certificate is hand-signed by H.M. King George V  or a facsimile signature of the king.  

(It looks authentic but I am not a pro at this.  We aquired our Royal collectible collection through elderly relatives of the collector who passed on.  She just wanted a garage full of treasures gone and we were blessed to receive the amazing treasures.)

2- A letter dated 22 November 1920 ( I believe this goes along with the other document -Grant of the Dignity.  The Letterhead reads:

CENTRAL CHANCERY OF THE ORDERS OF KNIGHTHOOD - ST. JAMES PALACE S.W.1  - It mentions Major J.H. Slayter