Assuming you are not using a Windows 8 tablet. I found that deleting the Adobe App (on the Modern or Metro "Tile side") and then re-installing the free App from the Store helped my problem that was similar. There are two other interrelated aspects which you need to consider: (1) Do you want PDFs to always open on the desktop side, or do you prefer that they open in a Live Tile App?, and (2) Do you want PDFs to open in the Internet Browser or in the Adobe Reader program on the desktop side?
You basically need to tell Win8 which of these options you prefer, we would need to know how you like to work with PDFs while blogging. When you follow a PDF link while in the browser, what way does the PDF open when things work the way you want them to?
One thing I know, there are up to 3 different "Default Program" settings for Acrobat Reader in Win8, even though they look the same. One instructs Win8 to always open the PDF in an App on the Modern/Live Tile App side. Another setting tells Windows 8 to override the Live Tile App and thus open every PDF on the Desktop (Windows 7) side. A third setting instructs Windows to open a PDF on the desktop side either (a) in the Acrobat application, or (b) open the PDF in a browser window. Here is the rub: You cannot open a PDF in the browser while on the Live Tile/Modern side. No plug-ins are supported on the Windows 8 App browser. The option for getting PDFs to open in a browser are in Acrobat Reader, not Internet Explorer or in control panel. (To see this swipe the Right side of the screen and hit the Search charm > If you have the Desktop program installed you will see "Internet Explorer XI" in the list on the left side of the page, click it (it will take a few seconds to open the full desktop program in the Desktop side) and Hit Control + K top open preferences > Go to Internet on the list > here you will find a link that says "How to set up your browser to use Adobe products to view PDF documents"