If you've upgraded to Quicken 2010 or newer from an earlier version, you may have noticed that the data file has increased in size without further data entered.
Unlike earlier versions, Starting in Quicken 2010, the data file structure for Windows no longer contains separate supporting files. (Supporting files have file name extensions like .QEL, .QPH, and .IDX.) Instead, the supporting files have been incorporated into a single Quicken data file with the .QDF file name extension. Also, if you have file attachments they are included in the single file as well. This simplifies the Quicken file structure and, as expected, makes it larger.