Question: In a Web application, is it possible to force a PDF file to be printed on the client? If the browser is configured to open the PDF inside the window, I guess that calling window.print() will work, but some browsers (like mine) are configured to open the PDF externally.

Answer: 
The way google docs does it is by embedding JavaScript into the PDF that tells Acrobat Reader or any other compliant reader to print it.

You would need a PDF toolkit to do this with a random PDF.
you can use the simple amazing library **printjs** "<http://printjs.crabbly.com>"
it takes PDF file and print it without showing print dialog if you need ,
a simple way to do it below :

```html
 <button type="button" onclick="printJS('docs/printjs.pdf')">
    Print PDF
 </button>
```