How to get the extended pdf version
pdf, version
Solution
PDF versions are 2 numbers only, X.Y. The existing PDF versions are 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 and 1.7. Starting with 1.7 Adobe added version extensions. The version extension information (a dictionary) is stored in the /Extension key in document catalog. The version extension dictionary has the /ExtensionLevel entry which can give you the 3rd number in your versions above. I assume you consider PDF 1.7 Extension level 3 as 1.7.3.
Problem
In the toolbar of adobe reader, in File->Properties->Description->PDF Version, you can only find the "big" version of pdf, but not the version extensions introduced by recent Adobe software. For example, if I have two pdf files, one is pdf 1.7.3, the other is pdf 1.7.5. In the file properties, I can only find pdf version 1.7. Does anybody know how to check the pdf version in details?