A Paper file disappeared? Everything is gone except few sentences.

That looks like a link to a file direct with Microsoft - does the file still exist there? Is the link still active?

I pasted the slide of PowerPoint which was saved in Dropbox, and the slide would disappear. After I downloaded to my computer and pasted the slide again, this did not disappear. 

Hi mlchiang, let's jump right into this! 

Just to clarify: do you have issues with a specific Paper document, or multiple ones? 

When did this start happening? 

You also mentioned a PowerPoint file, but I'm not entirely sure as to the steps you followed, and what you were trying to achieve. If you could elaborate, I'd appreciate it. 

Keep me posted!