Transaction files in QBO, QFX, OFX, QIF, MT940/SAT format are great for processing, but not so great for review like CSV or Excel files. Use the ProperConvert app to open, review such files and convert them to a conventional table format like CSV or Excel.
QBO/QFX/OFX files are offered in online banking to download transaction details. OFX files provide the date, amount, payee/payer, memo, check number, investment details for investment transactions. OFX files are also called "Microsoft Money" files.
QIF files are Quicken Interchange Format files containing details about transactions:
These files are provided by many banks to download transactions for your accounts. Files are not readable when are opened in Notepad or directly in Excel.
Here is a short video (1 min) showing the whole process of converting a QFX file to CSV format with QFX2CSV (replaced by the ProperConvert app):