You can create a file of any size using nothing more than what’s supplied with Windows.
Start by converting the desired file size into hexadecimal notation. You can use the Windows Calculator in Scientific mode do to this. Suppose you want a file of 1 million bytes.
Enter 1000000 in the calculator and click on the Hex option to convert it (1 million in hex is F4240.)
Pad the result with zeroes at the left until the file size reaches eight digits—000F4240.