While I'm a software author and can see that such could be created, we know DOCUMENT MANAGEMENT seems to be close to what you wanted.
HOWEVER!
I fear the cost of such systems would astound you. Maybe you can take a look at Google's Desktop Search to see if it will help you search said content.
I'm going with "I bet the cost would remove any system today from your grasp."
Bob
I have a large number of summary articles across a variety of topics.
I would like to be able to search these articles based on a number of different tags, and link each article to the sources it summarises (usually pdfs, but if I could link audio as well this would be a bonus).
For example, I have a summary of the US Primary process. This summary would be visible under tags such as 'elections' 'Republicans' 'voting systems'. Then, the summary would have a number of pdfs of source material attached.
Ability to sync across multiple devices would also be helpful.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic