That's because there is no conversion to do. From extremely early versions going forward, you simply install the windows version of FileMaker on the windows computer and then copy over your file. FileMaker for windows will open the file just fine and no conversion is needed or takes place.
But there are a few differences in how FileMaker works on the windows side so you might need to adjust a few layouts and maybe a few scripts.
Known cross platform issues:
Font substitution. If you used a font installed on the Mac that does not exist on the Windows machine, FileMaker will substitute a different font and the look of the layout will change accordingly. The substituted text may not fit the same space as the original causing text wraps and "clips" that did not occur in your original set up. If you used "plain vanilla" fonts, this should not be an issue.
Different Font Metrics. Windows systems require a bit more horizontal and vertical space to display the same text. Thus, you may need to "tweak" some layout text, buttons or fields to be a bit wider or taller before they look like they do on the Mac. (This is why I suggest designing layouts for cross platform systems on a windows machine. Moving from windows to Mac rarely has an issue in this area.)
No print scaling. If you use a scaling percentage to get a layout to fit the printed page on the mac, you'll have to redesign the layout by resizing the layout objects to fit the available print area as windows systems do not support print scaling. This may require creating a special copy of a layout used only for printing.
Window inside a window. If your solution opens multiple FileMaker windows, this is quite different on a Windows machine. On windows, all FileMaker WIndows open up inside a Application window. And if you have windows maximized when opening a new window, the existing windows drop out of maximized state and resize to what is often an unexpected size. It thus can take some extra scripting to manage windows on a windows system.
But note that none of these issues may affect you at all. It just depends on the design of your database.