Explaining any terms likely to be unfamiliar to laymen or specialists in other fields (most of the Monks, for example, or, at least, to /me anyway) when raising a question here (rather than, making us search for explanations) is helpful or even prerequisite if you hope for quick, on-target help.

Starting with the most nearly obvious:

• mzXML is an open data format for storage and exchange of mass spectroscopy data, developed at the SPC/Institute for Systems Biology.
• shimadzu is a tech corp which uses .gcd as a format for some of its mass spectrometers (and other tools?)
• .gcd is a file format used as above, and for digital architectural drawings and for map files for the like of Garmin's mobile/portable gps devices.

See I know what I mean. Why don't you? and please also note that most SoPW should demonstrate that you've made some effort to answer your own question. If you're stuck whilst coding, please include your code, error messages and warnings, etc.. as well as sample data.