Is Google Doc Viewer API - Free for Commercial Use?

For a long time, we are facing an issue in which our navigation menu hides behind the embedded pdf file.

Our issue is quite similar as mentioned in this question: Sub-menu is hidden behind PDF type object ( issue in Internet explorer)

For this issue, I found a solution to use Google Doc Viewer API & after using that API I found that our issue got fixed.

What we are using:

As shared in many articles & blogs that you can pass your URL of publicly available pdf file in query string parameter & this will render it perfectly.

• https://docs.google.com/gview?embedded=true&url=pdfURL

• http://docs.google.com/viewer?embedded=true&url=pdfURL

What I want to ask here a few questions regarding Google's this service.

I have not found this service mentioned on any official website of Google? Please find my questions below:

• Is it a valid google service that is available to use for everyone?
• Is it okay to use this service in a commercial web application?