The other convenient method of determining the file type is to use file identification tools. On Linux systems, this can be achieved using the file utility. In the following example, the file command was run on two different files. From the output, it can be seen that even though the first file does not have any extension, it is detected as a 32-bit executable file (PE32) and the second file is a 64-bit (PE32+) executable:
$ file mini
mini: PE32 executable (GUI) Intel 80386, for MS Windows
$ file notepad.exe
notepad.exe: PE32+ executable (GUI) x86-64, for MS Windows
On Windows, CFF Explorer, part of Explorer Suite (http://www.ntcore.com/exsuite.php), can be used to determine the file type; it is not just limited to determining file type. It is also a great tool for inspecting executable files (both 32-bit and 64-bit) and allows you to examine the PE internal structure, modify fields, and extract resources.