how to set a single password for multiple documents in PDF at one time.

I have Adobe Acrobat Pro DC (version 2015) (continuous) | 2015.017.20050

I followed these instructions form de website:  https://forums.adobe.com/thread/2167637

1- create an action by going into Tools > Action Wizard > create New Action

2- Under Choose Tools to add > Click Protection > Encrypt > and click on + sign to add this to the right-hand panel (uncheck the box next to Prompt user).

3- Then click Save & Export > Save> and add it to right-hand panel (you can change output options by clicking on specifiy settings)

4- Click Save and give action a name. (for ex: Batch password).

5 - Go to Action Wizard > Actions > Batch password

6- Click on Add Files> select all the files you want to add password to and click Start.

And it does  not work !

Acrobat Pro DC requires me to enter the password for each document !

I have 25 000 documents to insert a unique password.

Could you help me !

Sylvie Marchand