Hard Drive will not successfully recover PDF Files

I am trying to exhaust all options here, but I have a client's hard drive that needs data recovered. It had Windows XP installed and was having issues where it would boot up and the keyboard/mouse would not work. After trying to repair and the windows repair install would lock up, I ended up formatting the drive (after their approval), and reloaded windows. A few days later it seems data was on the drive that they forgot about.

I ran Ontrack Recovery Tools and found no existing folder structure. I ran Stellar Phoenix Windows Data Recovery and found folders with their old data (it created a C:\ Lost Folders ). However, when I try to recover PDF files that are needed, I get an error stating:
Acrobat could not open __ filename ___  because it is either not a supported file type or because the file is damaged.

I found some .pdf files doing a raw recovery from Ontrack and receive similar issues when trying to open these files (I tried to match some up based on file size.

So far I haven't opened one file which makes me think the drive somehow scrambled all of the data. Any other recommendations?