Assignment

The files can be found by looking in the database table mdl_files.

If you look for entries with 'component' matching 'assignsubmission_file' and filearea 'submission_files', then that will be the files uploaded to assignments.

If the 'filename' column isn't enough for you to then track the file down, then you will need to track down the correct submission in mdl_assign_submission, then match the id from that to the 'itemid' column in the mdl_files table.

Once you've found the record you want in mdl_files - make a note of the "contenthash" column, then look in your sever's "moodledata" directory, for the "filedir" directory. Then look for a sub-directory that matches the first 2 letters of the "contenthash". Within that sub-directory, find another subdirectory that matches the next 2 letters of "contenthash". Finally, within that directory, you will find the original file, renamed to match the whole of the "contenthash".

I'm not quite sure what you mean by "what format does moodle save such files" - the files are stored in exactly the same format they were uploaded (if you're using unoconv + PDF annotation, Moodle also generates a PDF version + PNG images of the pages, but the original file is stored unmodified).