Output several microstation sheet plots to one pdf?

Are these sheets in separate models? Separate drawings?

My recommendation would be to use the Print Organizer. Details can be found in the Help file.
Basically, you open the Print Organizer dialog and select the tool to Add Files to Set. Select the drawing(s) that contain the sheets you want. You will then be able to set all of your print options. If you have a predefined Print style you need to use, you can select it here, or you can choose Manually Specified Options...

This next dialog opens by default to the "Fence" tab, where you tell MicroStation how to recognize what you want to print. After you've done this, go through the rest of the tabs to set everything you need.

When you have everything set and you are ready to print, you can click the Print Icon. Make sure that you are using a PDF Printer Driver. Pay attention to the "Submit" portion of the dialog. You can submit as "Single Print Job" or "Separate Print Jobs" - you want "Single Print Job" for a multi-page PDF.

Thanks, Mary. That should take care of what I need..