Closing an external application with qt

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Hello everyone,
Please how do i close an application i previously opened with

QDesktopServices::OpenURL

QDesktopServices::OpenURL

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in qt c++.
Because i need to update text in a pdf i already opened outside my application at a point in time.
And also i would like to know the difference between

[DOCS]QDesktopServices::OpenURL[/DOCS]

[DOCS]QDesktopServices::OpenURL[/DOCS]

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and

[DOCS]Qt::openUrlExternally[/DOCS]

[DOCS]Qt::openUrlExternally[/DOCS]

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and basically when to use them.