How do I check the version of a PDF document?

Question

Is there some relatively simple method to determine a document's PDF version?
To be clear, I mean the document itself, not the application used to create it.
I'm trying to store PDF documents from external sources in a document repository.
Its manuals are unclear on Adobe Acrobat version support, although I have had problems with Acrobat v 9 in the past.
My source provided me with PDF documents that I was told were saved as versions 8, 9, 10 and 11 from Acrobat Pro XI.
Acrobat Reader XI is the only Adobe application I have and I don't want to write an application simply to confirm the PDF version.
When I open the documents using Reader XI and check their properties, I see the following:
nominal 8.0:  PDF Version 1.7 (Acrobat 8.x)
nominal 9.0:  PDF version 1.7 Adobe Extension Level 3 (Acrobat 9.x)
nominal 10.0: PDF version 1.7 Adobe Extension Level 8 (Acrobat X)
nominal 11.0: PDF version 1.5 (Acrobat 6.x)
The last one doesn't make sense, but I have another PDF saved as v 11 from Acrobat Distiller 11.0 that shows the same version in its properties.
So my questions:
1.  Is the Acrobat properties display accurate?
2.  I'm particuarly concerned about the 11.0 PDF documents since their Acrobat properties don't match the version they're supposed to be.
3.  Is there some other way to check a document's PDF version (other than writing an application), e.g., opening it with a text editor and finding a version string?

Answer 1

1. I have no reason to doubt it, the task is pretty simple.
2. You should realise that these are not rewrites but progressions. PDF 1.7 adds just a little to PDF 1.6, and so on. Early versions of Acrobat would always update the version number to the latest version, whether or not they needed to do so. More recent versions have got smarter. Sounds as if XI is smarter still and is writing the version number actally needed rather than just the highest number it knows. People have strange ideas about PDF version numbers and sometimes want to do things like "open and save in the latest version" but this is not just useless but meaningless.
3. In many cases the first line of the PDF contains the version number (but not the extension number), but this need not be accurate as a later piece of information (much later and harder to find) can override it.