@echo off
setlocal EnableDelayedExpansion
rem Create the list of default folders
set folder[888123]=999-888123-03
set folder[777456]=666-777456-01
rem Copy the files
for /F "tokens=1* delims=_" %%a in ('dir /B /A-D *.pdf') do (
copy "%%a_%%b" "!folder[%%a]!"
)
EDIT: The version below don't need to initialize the list of default folders:
@echo off
for /F "tokens=1* delims=_" %%a in ('dir /B /A-D *.pdf') do (
for /D %%d in (*_%%a_*) do (
copy "%%a_%%b" "%%d"
)
)