This tutorial explains the difference between OFX file and QFX file. Quicken imports QFX files and does not import OFX files. Quicken set QFX file description as "Quicken OFX data" creating great confusion for its users that believe they need OFX files it import their data.
Some confusions, that you may see when you work with QFX file. OFX file has .ofx extension and the QFX file (Web Connect File) has .qfx extension. Quicken marks them, when you install Quicken on your computer, register Doc files as Quicken OFX files. So you can be easily confused, that the .qfx file is actually an OFX file, but it is not. QFX file is Quicken Web Connect File, which Quicken calls Quicken OFX data file. Quicken doesn't import OFX files. It imports only .qfx files. But Quicken calls them Quicken OFX files. So when you use some converters, for example, ProperSoft CSV2QFX converter and you convert CSV to QFX and you'll get the .qfx file, but you'll see in the file explorer, that it's called Quicken OFX data file, if you have installed Quicken on your computer. Don't be confused by this description here. IMPORTANT: CSV2QFX is now replaced with the Transactions app, which converts from more formats and converts to more formats.