PDF Library Manager Suggestions?

[canpolat]

I have scanned some of the very old books I had (which are unlikely to be published as e-books in the near future) and am looking for a tool to keep track of them (and hopefully add some additional metadata which is not possible to add directly into the files).

Calibri, I guess, is the first tool that comes to mind. But its strict folder structure renders it unusable to me. I want to keep all my files in a folder (or construct my own structure, but I don't want the hierarchical structure dictated by a Calibre). Here are some initial requirements:

The tool is able to:

1. Scan a folder and index all the PDF files in that folder
2. (Optional) Parse the metadata of the PDF files
3. Keep additional metadata entered by the user (fetching from web s also OK, but for the books I have I doubt it will be of any use)
4. (Optional) Update relevant metadata according to user input

Support for no other file format is required. Ideally the tool should be free software (as in freedom).

Any suggestions?

[canpolat]

The only tool I could find so far is eLibrary (http://openelibrary.org/). But it has many problems:

1. It doesn't seem to be maintained any more. And the latest source code on the development branch doesn't even compile in Visual Studio 2012 (it may compile with an older version, I haven't checked it).
2. The user interface is not intuitive at all: it has many useless steps when importing data from the web (Google Books); you have to click through all the books when importing a folder so importing folders with many files is very difficult.
3. Some of the tool-tips are missing and some of them are wrong. This makes the UI even more confusing.

It looks like the developer put quite some effort into this project, but didn't have time to clean things up. Perhaps it may be useful for very small libraries. I'll keep looking for alternatives...