PDF Comments and Google Docs

PDF (the "universal format") is not a Google Doc. Or, if you will, a Google Doc is not a PDF.
Yes, Google Docs does support upload of PDF (and other formats) - for viewing.
Because PDF is an ISO Standard (ISO 32000) Google may decide to invest the time/$ in producing an application like Acrobat.
Google has added a PDF viewer to Chrome.
But, until there's a - what? Googlebat? - to do what you want I suggest you do a shared review and make use of Acrobat XI / Adobe Reader XI.

To perform a shared review of a PDF use Acrobat.com or an internal server.
Acrobat's Help provides a brief discussion of this.
Adobe TV has videos the depict the fundamental "how-to".

Inform the user who does not have Acrobat to download and install Adobe Reader XI. Reader XI has the same Comment and Mark Up tools you find in Acrobat.

Be well...

Google Chrome Browser can File out Forms from websiteand saved or sent PDF work just as well in Reader.

Chrome apparent seems to use its own PDF system. I've tested fillig out forms within website and works great.

And I  have many PDF on my own website until  just a few years ago I could click on button I have in a PDF Plugin called PDF Browser Plugin by Schubert That allowed for filling out forms and and Clicking Buttons They No longer work after the switch to Mountain Lion (OSX.8.x) The Acrobat Plugin hasn't worked in years on the Mac and there is no interest in fixing it. So the only way to view PDF within a Browser and fill out forms or cause buttons to work, is Chrome or Maxthon (a cloud based Browser Based on Chrome)

There No Mozilla Support.

If opening Reader will work, but requires downloading a new copy of the File everytime file is opened in Browser rather than as the browser plugin does opens in Chace and once finished the PDF disappears.

As I'd mentioned, PDF is one of the file formats Google Docs supports for upload.
To provide you a view of the PDF page content  Google Docs presents one with the renderable characters in a Google Doc viewing format.
If you convert a PDF to a 'real' Google Doc the result is an image of the PDF's page content.
In either situation you are not viewing the actual PDF; rather you are viewing a representation of what Google Docs can extract.
How good a representation of the PDF page content is depends on the quality of how the PDF was produced.

Example:
Some PDF producers make use of font encoding that is customized or non-standard.
Consequently such does not map properly to Unicode. So, what is extracted for presentation can be rather different then what is 'seen' in the PDF. 

Back to the PDF page content. You'll note I've made use of the phrase "page content" often. That is what Google Docs extracts for presentation.
Comments and Markups are PDF annotations. Annotations are not part of a PDF's page content.
(This is described in the ISO Standard for PDF, ISO 32000.)
Consequently annotations are not extracted by Google Docs.

There are several ways to get a shared review of information done.
Google Docs, Adobe's Creative Cloud, Microsoft Office applications and Skydrive and so forth.
But, as mentioned in my earlier post, if it is a "must" / "need" / "preference" to perform a shared review with PDFs then you use:

--| Acrobat.com (workspaces)

--| Internal Server

--| Current version of Microsoft SharePoint

One would be using Acrobat (XI first choice, X second choice) or Adobe Reader XI.

n.b., the orginator of the shared review should be using Acrobat Pro.

If none of these three environments is desirable to use then the shared review will have to make use of something other than PDF.

Currently these 3 are know reliable for working with "live" annotations (Comment / Mark up tools of Acrobat or Adobe Reader XI).

Be well..