From Intelligent Converters:
Verovio supports conversion from MusicXML to MEI. When converting from this web interface, the resulting MEI data will be displayed directly in the MEI-Viewer. Jun 06, 2014 Not sure which PDF facility within MuseScore you are talking about. There is nothing built in to MuseScore itself. But the musescore.com score sharing site.does. incorporate a PDF conversion facility, powered by Audiveris, the open source PDF-to-MusicXML converter. It works reaosnably well, if your expections are set appropriately low.
PDF-to-XML is a program that converts Adobe PDF documents into XML format. The resulting document is compatible with XML 1.0 and higher. Features: Adobe Acrobat or Reader is not required; option to customize XML tags in the resulting files; recognizes tables; converts individual pages; command line support; Unicode support; easy-to-use wizard-style interface; full install/uninstall support.
What do you need to know about free software?
From Intelligent Converters: PDF-to-XML is a program that converts Adobe PDF documents into XML format. The resulting document is compatible with XML 1.0 and higher. Features: Adobe Acrobat or Reader is not required; option to customize XML tags in the resulting files; recognizes tables; converts individual pages; command line support; Unicode support; easy-to-use wizard-style interface; full install/uninstall support.