Use a flexible file format. My preference is .csv, because it can be read by almost any program. I'll tolerate .xls, but I'm not pleased with .xlsx (not everyone uses Excel!). And please, please, please do not use pdf.
Why is .xls tolerated but not .xlsx?
XLS and XLSX are both Excel formats, but XLS is a binary blob while XLSX is just a zip containing xml files. I'd much rather parse xml files (XLSX) than the binary blob of XLS.
Why is .xls tolerated but not .xlsx?
XLS and XLSX are both Excel formats, but XLS is a binary blob while XLSX is just a zip containing xml files. I'd much rather parse xml files (XLSX) than the binary blob of XLS.