How can I download additional extension not supported in mobile safari?

Qrafter is iPhone application to read the QRCode. (http:/开发者_运维知识库/itunes.apple.com/us/app/qrafter-qr-code-reader-generator/id416098700?mt=8).

if Qrafter is installed in your iPhone and you click a Vcf extension file in mobile safari, iPhone will launch the Qrafter and read the Vcf file! (Vcf is not supported extension officially in mobile safari)

How can I develop this function like this?

Well this is just a support File Type for your application. Apple has a nice document about it: https://developer.apple.com/library/ios/#documentation/FileManagement/Conceptual/DocumentInteraction_TopicsForIOS/Articles/RegisteringtheFileTypesYourAppSupports.html#//apple_ref/doc/uid/TP40010411-SW1

It's not an extension of mobile safari.