Use the Sensitivity feature in Office to apply sensitivity labels to PDFs: registry value disablepdfprotectionUserHKCU\software\policies\microsoft\office\16.0\common\fixedformat

Policy ID: L_PDFProtectionFromOffice
Scope: User Configuration
Supported on: At least Windows Server 2008 R2 or Windows 7
Source: Microsoft 365 Apps / Office Administrative Templates (version 5568.1000)
Category: Microsoft Office 2016 › Microsoft Save As PDF and XPS add-ins

Registry

disablepdfprotection

REG_DWORDUser

HKCU\software\policies\microsoft\office\16.0\common\fixedformat Current key

Enabled value: 0
Disabled value: 1

Apply with .reg · CMD · PowerShell

.reg

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\common\fixedformat]

; Options (use only one)
; Enabled
"disablepdfprotection"=dword:00000000
; Disabled
"disablepdfprotection"=dword:00000001

CMD

:: Options (use only one)

:: Enabled
reg add "HKCU\software\policies\microsoft\office\16.0\common\fixedformat" /v "disablepdfprotection" /t REG_DWORD /d 0 /f
:: Disabled
reg add "HKCU\software\policies\microsoft\office\16.0\common\fixedformat" /v "disablepdfprotection" /t REG_DWORD /d 1 /f

PowerShell

# Common: create the key
New-Item -Path 'HKCU:\software\policies\microsoft\office\16.0\common\fixedformat' -Force | Out-Null

# Options (use only one)
# Enabled
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\common\fixedformat' -Name 'disablepdfprotection' -PropertyType DWord -Value 0 -Force | Out-Null
# Disabled
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\common\fixedformat' -Name 'disablepdfprotection' -PropertyType DWord -Value 1 -Force | Out-Null