We have found one software suitable in our database for this conversion.
STATISTICA analytics tool offers users direct import and export capabilities for Microsoft Excel formats, so a sta to xls conversion seems to be possible.
It basically represents export of data spreadsheets (.sta) to Excel spreadsheet (.xls, .xlsx). Most likely done through some export function found in the program.
STA
Files with sta extension may be typically encountered data spreadsheets from StatSoft Statistica software. Default file type.
XLS
Files with xls extension are best known as spreadsheets from Microsoft Excel. A spreadsheet is basically a grid of cells sorted in rows and columns. Each cell can contain text, numeric or formula data. Excel XLS spreadsheets can be opened in most other similar programs, such as OpenOffice.org Calc.