Hi Chris,
Thank you for your interest in Syncfusion products.
Essential XlsIO can only preserve macros in Template files. This means that you would have to define the functions in VBA using MS Excel and cannot do it during runtime using XlsIO. For example, you can have a spreadsheet that can have macros in it and then use XlsIO to open these spreadsheets as a template and make modifications to the spreadsheet. When this modified spreadsheet is resaved using XlsIO the macro is retained.
Here is a sample that demonstrates macro usage in XlsIO
http://www.syncfusion.com/Support/user/uploads/VBA_b814797b.zip Please let me know if you have any other questions.
Best Regards,
Bhuvana