Fulcrum PDF reports are named with the record's unique fulcrum_id. This bash script loops through the parent CSV file and renames the PDF files based on the index of user-specified fields.

fulcrum-report-rename.sh

#!/bin/bash
INPUT=fire_hydrants.csv
OLDIFS=$IFS
IFS=,
[ ! -f $INPUT ] && { echo "$INPUT file not found"; exit 99; }
while read -a csv_line
do
	mv ${csv_line[0]}.pdf ${csv_line[8]}-${csv_line[0]}.pdf
done < $INPUT

windows-cmd-rename.txt

FOR /F "usebackq tokens=1,2,26 delims=," %a IN (fire_hydrants.csv) DO ren %a.pdf "%c.pdf"

windows-rename-append.bat

REM This batch script appends first 10 characters of the value in the second column of the .csv (Fulcrum's `Created At` date value) to the front of the `fulcrum_id.pdf`
@echo off
setlocal enabledelayedexpansion

FOR /F "usebackq tokens=1,2 delims=," %%g IN (inspection_reinspection_count.csv) DO (
	set sub=%%h
	set sub=!sub:~0,10!
	ren %%g.pdf "!sub!-%%g.pdf"
)

windows-rename.bat

:: this Windows batch file will rename a folder of PDF's from the Fulcrum Exporter using a column from a CSV, typically exported from Fulcrum
:: copy this code and paste it into Notepad, save the text file to your extracted export folder with the extension .bat instead of .txt
:: edit line with "tokens=1,2". '1' is the fulcrum_id/_record_id column and the first CSV column ...you probably don't want to edit this
:: '2' is the second column of the CSV ...update this with the column number which you want to rename the PDF to
:: edit 'rename.csv' to the name of your Fulcrum exported CSV
:: this script currently doesn't handle renaming-to values containing commas - you must manually remove them like with Find/Replace in Excel or similar
:: you may want to manually 'build' your own filename field in your app with a hidden Calculation field and/or Data Event

@echo off
setlocal enabledelayedexpansion
echo I will now try to rename things, shall we begin?
pause

set /a counter=0

FOR /F "usebackq tokens=1,2 delims=," %%a IN (rename.csv) DO (

	:: rename the fulcrum_id.pdf with the values in the 2nd column of the CSV
	IF EXIST %%b.pdf (
		ren %%a.pdf "%%b_!counter!.pdf"
	) ELSE (
		ren %%a.pdf "%%b.pdf"
	)

	:: next line is for debugging
	:: echo %%a.pdf "%%b.pdf" >> results.txt
)