According to this document  https://support.atlassian.com/confluence-cloud/docs/display-files-and-images/
Currently, the only option with a Confluence cloud page attached PDF file is 

• Change view — Display the file inline or as a thumbnail.

• Preview — Open the file in viewer mode.

• Download — Download the file to your computer or device.

Customers would like to have an option to center align a PDF file as well like images.