Why Google Viewer
sometimes is opening a blank page instead of open the PDF file?
I could simulate it using this code. It doesn't happen every time. It will be necessary to click on the Google Viewer button few times.
I could simulate it on Edge and Chrome.
Pay attention to the two tabs after the tab title "Sem títlulo". They opened the PDF file perfectly. However, the tab with the title "Sem título" did not open the PDF.
EDIT
I'm using google docs viewer https://docs.google.com/viewer.
window.open()
does... unless you configure it not to with the windowname argument. – Chacon