您不能这样做，除非您自行注册它也可以打开PDF文件.然后，如果PDF Expert可以选择在另一个应用程序中打开文件，则用户将可以再次打开它.

You can't, unless you app registers it self that it can also open PDF file. Then if PDF Expert has an option the open the file in an other app the user will be able to open it your again.

iOS SDK中没有内置功能，可让您从其他应用程序获取文件.

There is not build in feature in the iOS SDK that lets you get a file from an other app.