Import others file type (pdf, ppt, xlxs) when using import word documentat operation shows stack trace error

Description

When using the Import word document feature and attach other file types such as pdf, ppt, or xlxs, it will redirect the user to a page with the error stack trace.

Steps to reproduce

1. Login Confluence
2. Open a confluence page
3. Click the (...) to show the dropdown menu
4. Select Import Word Document
5. Attach a pdf file
6. Clcik Next
7. Click Import
8. An error stack trace is show to the customer

Actual Result

Suggestion

1. It will be better if confluence can verify the attached file is word file before proceeding to the next steps
2. Redirect user to a proper error message rather than showing error stack trace.