While the name starts with the letter "f," the grammatical rule for choosing between "a" and "an" depends on the of the first letter. In English, the letter "f" is pronounced starting with a vowel sound ( "ef" ).
The proper article to use before is "a." farm_boy-win32-x64.7z
"farm_boy-win32-x64.7z" (If you are spelling out the letters: "ef-ay-ar-em..." ) While the name starts with the letter "f,"