As per your description above, you had a action created to remove the encryption from the multiple files with same password. Could you please share the video tutorial link that you are referring above?
To remove the encryption from the file, please use the steps to create an action.
- Launch Acrobat and go to Tools > Action Wizard > New Action.
- In Create New Action window, select Protection > Enrypt
- In Specify settings at right, select None and save the action.
- Now open the PDF and then Action wizard
- Select the action from the list at right and click on Start.
- In the Document Security select None and close the window.
Check if that helps.
Let us know if you need any help or experience any issue.