Thanks for your posting and using Aspose APIs.
This is possible. First you will hide all the worksheets except your selected sheets and then convert your Xlsb to Pdf.
You can hide the worksheet with the following code.
//Hide this worksheet
Worksheet ws = ..;
ws.IsVisible = false;
We have also added a New Feature request to fulfill your needs directly without any workarounds. We will implement it if it is feasible for us. Once, we will have some news for you, we will let you know asap.
This issue has been logged as
CELLSNET-45761 - Save Selected Worksheets to Pdf