Can a PDF file be displayed on a dashboard page?

Did you try embedding it as an image within a rich text field on the dashboard?

This isn't really a great idea as pdf documents are typically a full 8.5" x 11" page and simply don't embed well. Nevertheless you can create a HTML code page referencing your pdf URL and embed it as a web page widget using markup similar to this:

<object data="https://eforms.state.gov/Forms/ds11.PDF"; type="application/pdf" style="width:100%;height:1600;">>
    <iframe src="https://docs.google.com/viewer?url=https://eforms.state.gov/Forms/ds11.PDF&embedded=true"&g...;
</object>

But you will probably have problems with the double scroll bars and need JavaScript to resize the <iframe> to match the size of the contents.