There are some web-based services such as converting .flv files into .mp3 files, .doc files into .pdf files, etc. These are the servers that take files from the user and apply respected applications (such as conversion). After that, the converted file may be available to the requested user.
Please provide me some keywords for this as I do not know what to google for.
Well for PDFs this can be done using entirely PHP. See http://www.php.net/manual/en/book.pdf.php for the PDF functions and http://uk.php.net/manual/en/pdf.examples-basic.php for some examples of usage.
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