How to Fix the HTTP File Upload Error in WordPress?

How to Fix the HTTP File Upload Error in WordPress?
Today, I encountered an HTTP error when uploading file (a pdf) to WordPress website. While editing a post or page, on clicking 'Add Media', the file seems to upload as the progress bar progresses but after a while WordPress shows HTTP error. In this post, I would like to share how I resolved or fixed the HTTP File Upload Error in WordPress.