Word slow to open .docx files

I received a Word 2007 .docx file from someone, but the file took more than 30 seconds to open. I suspect there is something in the document that is corrupted.

Here’re the steps that I did to fix the problem.

1. Create a new blank document.
2. Select all the content in the problematic document.
3. Copy and paste in the new document.
4. Save the new document under a new file name.
5. Close and re-open the newly created file.

The file now opens almost immediately.