How to see all the bits of a file?

I'm looking for a way to see all the bits of a file. I want to see all the 01's in my file, because I want to know what changes exactly happen when I edit a file using a closed-source application.

Use a hex editor like @ChrisF suggests. A good one for Windows is "HxD."

Please note that generally computers deal with multiples of 8 bits at a time unless interfacing directly with hardware (and most of the time even then). So looking at a file divided on those boundaries is usually better and more meaningful than just a raw stream of 0s and 1s.

Learn about hexadecimal and how it relates to binary first. It's really pretty simple (0 = 0000, 1 = 0001, 2 = 0010, ... 9 = 1001, A = 1010, B = 1011, C= 1100, D = 1101, E = 1110, F = 1111)

Also, comparing the files by hand is likely to be tedious. You'll probably need a tool like BinDiff, vbindiff, or similar.

HxD doesn't really see the bits, it shows bytes in hex, dec and oct.

Bytes and Bits Viewer : this little executable does the job, let us open a file, watch its bytes in hex and in BITS (yeah!, ones and zeroes), download for free:

http://www.softpedia.com/get/Programming/File-Editors/Bytes-and-Bits-Viewer.shtml#download

What good is this program for? Well, in my case, I made a program in assembly 8086 to compress files using Huffman (https://stackoverflow.com/questions/30198324/i-have-trouble-building-codes-for-frequency-table-in-huffman-compression/30200096?noredirect=1#comment48507449_30200096). To check if the resulting file was fine, I used Bytes and Bits Viewer to see the ones and zeroes in the Huffman codes.