Actually when you open a .PDF page, e.g: http://192.168.1.2/yourFile.pdf, the browser is served as a PDF viewer instead of an actual webpage. Therefore you can’t “spy” or “record” anything on this PDF file due to this fact.
For ‘Verify PDF’ keyword, please refer to this guide to build your custom keyword : http://www.testingdiaries.com/selenium-webdriver-read-pdf-content/