Word generates code that is hidden in your Word document to enable it to communicate with EndNote. This makes the file size a lot larger and many publishers request that you remove this code when you submit your paper for publication. You should also remove the code when submitting a paper to Turnitin, UCL's plagiarism detection software.
You should only remove the code when you are sure you have finished editing your document.
Do not delete your original document with the field codes retained! To edit your references once the code has been removed, you must edit the original copy of the manuscript and then remove the code again.