If you have the original password, you can permanently remove it by going to Tools > Protect > Encrypt > Remove Security .
If you are hesitant to install new software, there are other reputable ways to manage PDF security: Download FaresCD Com Pass Fab for PDF zip
It supports files created by Adobe Acrobat and other popular PDF tools across various encryption types. How to Use the Official Tool If you have the original password, you can
Sites like pdfforge allow you to remove passwords in a browser without downloading software, provided you know the current password. PassFab for PDF Review - How to Use PassFab for PDF If you have the original password
If you remember parts of the password, the Mask Attack is usually the fastest option.