Renaming a file with spaces in the name will give you an error when using a DOS Prompt or Command Prompt.

When using a DOS prompt or command prompt and trying to rename a file that has spaces in the name, my file.txt will result in an error.

Perform the following action in a command prompt
Substituting the U:\Files For your actual drive and folder path.

U:\Files\rename my file.txt my file.doc
The command syntax is incorrect.

To properly write out the DOS command to rename your file with spaces, perform the following action. This command will come in handy if you are unable to rename the file in Windows because it is in use.
U:\Files\rename my?file.txt my?file.doc

As you can see above, we have added a Question Mark ? In place of the spaces in the name of the file.
What this does is give a legal DOS filename character.

If you leave the ? mark off from the output filename like this
U:\Files\rename my?file.txt my file.doc
The output renamed file will be my file.doc
See, the ? in the original filename adds an underscore to the output filename.

But adding the ? to the output filename lets you rename the file with the original space still intact.