I will try to help a little bit:
The New Zealand Expeditionary Force (NZEF) was the title of the military forces sent from New Zealand to fight for Britain during World War I.
This NZEF had 3 subunits (brigades) and a divisional unit; Each brigade has subunits as well:
1. New Zealand Infantry Brigade
- Auckland Battalion
- Canterbury Battalion
- Otago Battalion
- Wellington Battalion
- 1st New Zealand Infantry Brigade Signal Co.
- New Zealand Field Ambulance No. 1
2. New Zealand Mounted Rifles Brigade
- Auckland Mounted Rifles
- Canterbury Mounted Rifles
- Wellington Mounted Rifles
- New Zealand Engineers Field Troop
- New Zealand Mounted Signal Troop
- New Zealand Mounted Rifles Field Ambulance
3. New Zealand Field Artillery Brigade
- 1st Field Battery
- 2nd Field Battery
- 3rd Field Battery
- 1st Brigade Ammunition Column
4. divisional cavalry
In 1916 NZEF was raised to divisional strength; it now consisted of the 1st NZ Infantry Brigade, the 2nd NZ Infantry Brigade and the 3rd NZ Rifle Brigade.
As many soldiers had died in the war, reinforcements were set up in NZ to replenish the decimated units.
The 25th Reinforcements (38 officer, 1816 other ranks) sailed towards the European theatre of war on 26 April 1917. For organisational reasons, they were naturally divided into battalions and companies.
That means that your ancestor was in the D-company of this 25th RFTS.
And this unit reinforced the NZ two Infantry brigades and the NZ Rifle Brigade.
If you mention Otago Battalion and B-Company, your ancestor was one of the soldiers who came after arriving at the theatre to the B-company, 1st Otago Battalion, 1st NZ Infantry Brigade of the NZEF.
If you are not so familiar with military matters, here is a short, general overview for NZ in WW I
- 1 division consisted of 3 - 4 brigades
- 1 brigade consisted of 4 battalions
- 1 battalion usually from 4 companies
- 1 company was then divided into platoons and squads.
To the rank of your ancestor:
Pte means Private; Rfm, Rfn means Rifleman.
All ordinary soldiers were called private, but private soldiers had different names when they served or were trained in different units.
A Rifleman is a special kind of Private. Higher ranks were corporal, sergeant etc.
For more information read:
https://nzhistory.govt.nz/war/infantry-units and
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwivmuXP_YvtAhWIHRQKHc4MC2sQFjACegQICBAC&url=https%3A%2F%2Fnzhistory.govt.nz%2Ffiles%2Fdocuments%2Fww1-stats%2Fprovision-and-maintenance.pdf&usg=AOvVaw2DqGcE_z2b_2xb9Bp4rEuX (pdf-Document)