Q:

How to show pdf files to user's browser,in the case of no plugin is installed

how can we show pdf document in users browser.In the case the plugin is not installed.
Is google api for pdf is usefull in this case?

A:

Google provides a tool to do this:

Option 1 - Generate your users a link:
https://docs.google.com/viewer?url=my_domain.com/my_pdf.pdf
Option 2 - Embed into page so that users stay on your site:
<iframe src="https://docs.google.com/viewer?url=my_domain.com/my_pdf.pdf&embedded=true">

