Open the PDF in Adobe Acrobat Pro
Go to File
Select Properties
Open the Security tab
Choose No Security from the Security Method menu
Enter the document password if prompted
Save the PDF
Open the PDF in a browser or PDF reader if it allows printing
Print the document to a new PDF file
Save the new PDF without a password
Use an online PDF unlock tool
Upload the PDF
Enter the password if required
Download the unlocked PDF
Use a PDF password removal app
Open the protected PDF
Remove the password protection
Save the unlocked file
If you do not know the password, ask the owner for the password or an unlocked copy