Why should PCB files be converted to GERBER files and drilling data after PCB copy board is submitted to PCB factory for board making?
Most engineers are accustomed to send PCB files directly to PCB factories for processing after designing, while the international popular practice is to convert PCB files into GERBER files and drill data and then hand them over to PCB factories, so why do we need to do this?

Because electronic engineers and PCB engineers do not have the same understanding of PCB, GERBER files converted by the PCB factory may not be what you want, such as your design will be the parameters of the components are defined in the PCB file, you do not want to show these parameters in the PCB finished products, you did not make a description of the PCB factory to follow the zucchini will be left on these parameters on the PCB finished products. This is just an
example. This can be avoided by converting the PCB file to a GERBER file yourself.

GERBER file is an international standard optical drawing format file, which contains RS-274-D and RS-274-X two formats, of which RS-274-D is known as the basic GERBER format, and to be accompanied by a D-code file in order to fully describe a graphic; RS-274-X is known as the expansion of the GERBER format, which itself contains a D-code information. Commonly used CAD software can generate these two formats.

How to check the correctness of the generated GERBER after PCB copying?
You can simply import these GERBER files and D-code files in the free software Viewmate V6.3 and see them on the screen or print them out on a printer.

Drill data can also be generated by various CAD programs, usually in Excellon format, and can be displayed in Viewmate. Of course, you can’t make a PCB without drill data.