The rear of a large format camera has a ground glass. (It is this distinctive part which make us fun looking at under the dark cloth...)
The principle is that the matte surface of the ground glass occupies the exact place the film will be. So if your image is in focus on the GG it will be in focus onto the film.
Now, to hold this film you've several solution :
First use the international film holder (made by Fidelity and the likes) which holds one sheet of film fer face;
Or use the Grafmatic and associates which is a box holding 6 sheet of films each in a separate thin metal holder
Or use film individually packed in paper be it Polaroid or Kodak Readyload or Fuji QuickLoad. For this film you need a holder to have the correct placement of film as the paper is thinner than the plastic/metal of the two first solutions. *
You see that the packaging of the film is irrelevant, only it's position matters. (and to a lesser extend the thickness of the film holder because it has to fit in the back in place of the GG so if it is too thick, the ground glass won't retract enough to make room for it. )
The Graflock system is used to position a roll film holder on the camera's back to take "small pictures" on a large format camera.
A search will give you the ANSI specs for the film holders and the film sheet placement inside it. Only two surface are important (and their relative placement) :
The first one is the one that sits on the camera back, where the GG was before insertion of the film holder, the second one is the surface of the sheet of film ready for exposure. This surface is inside the film holder you plan to make/use.
Hope this clarify the matter ;-)
* There is instant film in pack. But not in 4x5 format (IIRC). the principle is the same, you put the pack in an holder which will place the first film to be exposed at the very same surface the GG was. Then there is a way to select another sheet of instant film when the one you exposed had been put off to develop and see.