Why does the file size change when you change the "open with" option in Get Info? Create a plain text file with the string ABCDEFGHIJKLMNOPQRSTUVWXYZ.
Check the file size. It is 26 bytes, as expected.
Go to Get Info, and find the pane labeled "Open with..."
It says "TextEdit" by default.
Change it to something else. I changed it to "Microsoft Word".
Boom. The file is now suddenly 1,364 bytes (8 KB on disk) large.
Now I will change the box back to "TextEdit".
It stays at 1,364 bytes.


So my question is, what exactly happened here?


Why did the file size grow when I changed the program that opens it?
And why did it not revert when I changed it back to the default? How do I revert it?


If you open the file, the string content is intact. So, how exactly are all those extra bytes being used? If OSX says that it is 1kb large, then surely there is 1kb of stuff in it?

OSX Mountain Lion.
Not sure but it MIGHT be the MS Word icon that takes the extra space.

Try this, get info on the file after you have changed it back from an MS Word document.

Click on the icon in the upper left corner

Press COMMAND-X (cut)

close the window

re-open it and see what the size is....

Just spitballing here...