Hi,
From Supported File Formats|Documentation
It looks Aspose.Cells is not supporting XLA files So, can you please help with the question that whether I can load a XLA file and convert it into XLSM?
Please note, XLA and XLAM are MS Excel Add-Ins that add modules or extra functions/tools to Microsoft Excel application. Aspose.Cells does support to set add-ins functions via specific APIs. See the document on how to set/use Add-ins functions for your reference: