There are many ways of doing this. The PDF document that can be generated with Mendix have limited styling options.
Have a look at https://appstore.home.mendix.com/link/app/114043/ which can generate a PDF from a Mendix page.
On the page you can use charts, image and CSS styling for tables with rounded and custom borders and make a PDF out of it (sever side)
You might want to create a seperate PDF document with only the borders and upload that to your environment. You can then merge this document with the one that is generated in Mendix. Look at the community commons for the Java actions to merge two PDF documents.