1. Enter the reading page and tap Editor on the toolbar;
2. Choose Set Passwords and set Open Password, after that, you can set The permission to restrict printing and copying of the document, And you should select at least one encryption level first;
3. Tap Batch to set passwords for multiple PDF files;
4. Click + Add Files to add more files, if you want to remove one of the added PDF files, click , if you want to remove all added files, click Remove All;
5. After setting your passwords, click Encrypt to finish your security setting.
Or you can find Security in Quick Tools on Home to quickly encrypt PDF files.