In Paper Mario: The Thousand-Year Door's root file structure, the game's tile texture graphics is stored in root/b.
The tpl format is a compressed file format that contains .tga files, which can be opened by most graphical editing programs.
root/b
There are more than a dozen tpl files in the folder, and are assigned japanese names which indicate which tpl file holds which textures.
aaa (Mario Bros.' House, and prologue or “pro”)
aji (X-Naut Fortress) (“stg7”)
bom (Fahr Outpost) (“stg7”)
dmo (Opening Demo) (“op_book” + “op”)
dou (Pirate's Grotto) (“stg5”)
eki (Riverside Station, interior) (“stg6”)
end (Staff Credits)
global (Menus, tattles, and mail)
gon (Hooktail Castle) (“stg1”)
gor (Rogueport)
gra (Twilight Trail) (“stg4”)
hei (Petal Meadows) (“stg1”)
hom (Riverside Station, exterior) (“stg6”)
jin (Creepy Steeple) (“stg4”)
jon (Pit of 100 Trials)
kpa (Bowser)
las (Palace of Shadow) (“stg8”)
moo (The Moon) (“stg7”)
mri (The Great Boggly Tree) (“stg2”)
muj (Keelhaul Key) (“stg5”), also includes all dialogue at sea
nok (Petalburg) (“stg1”)
pik (Poshley Heights + Poshley Sanctum) (“stg6”)
rsh (Excess Express) (“stg6”)
tik (Rogueport Sewers)
tou (Glitzville + Glitz Pit) (“stg3”)
usu (Twilight Town) (“stg4”)
win (Boggly Woods + Flurrie's House) (“stg2”)
yuu (Pianta Parlor)