Support for Macro-enabled Files
Macro-enabled Excel files (xlsm) can be previewed in Box (albeit a little slow to generate preview), but macro-enabled Word files (docm) cannot be previewed.
Neither document type is officially listed as a supported file type (https://community.box.com/t5/Managing-Your-Content/What-file-types-are-supported-by-Box-s-Content-Preview/ta-p/327), so it would be expected that both work the same way (either be previewable or not).
Macro-enabled Office files have been around now for a while. Support for them should be added to Box preview.