Yesterday I had to compare to xlsx files. When decompressing all the files (xlsx files are just zip files), the content was identical. Something was different at at the zip level. How do you identify that difference? Easy.

1. Compare the two files with https://hexfiend.com to highlight the differences.

2. Open the file in https://ide.kaitai.io and go to the identified offset to figure out the meaning.

Here the difference was in the "version made by" field.