Actually I don't think you can.
Just add 2 or more seperate text lines.
This is a long standing request on Mentor Ideas forum.
You can vote for it if you like!
It is possible to write some text in for example Word and then insert this as an object into PADS.
But this text is not available for Gerber data - if this is what you want.
One clumsy workaround is that you can select single line texts and combine them into one entity. I use this for my design notes so I can pull the entire set from the library with one operation.