Add 'Close File' Function

[hairycactus]

Current Behaviour

If a window is loaded with a PDF file that subsequently requires no user action, there is no way to view a new file, unless we ...

1. Delete all PDF pages on the existing window, before loading a new file via the Open File & Append to Current Document button.

• Not ideal, because the window retains the metadata properties of the "previous" file (whose pages have been deleted).

2. Open a new window via ☰ > New Window (CTRL-N) & load the file there.

• Not ideal, because closing the unwanted 1st window causes PDF Arranger to exit abruptly -- see Closing 1st Window causes Program Exit when Multiple Windows are Open #592.
• Even the said issue doesn't exist, opening a new window & closing the previous window just to discard a file & open a new file is not just annoying workflow, but also results in additional workload for the host system.

Desired Behaviour

There should be a Close File function for each open window. And after the file is closed, the window should not retain any metadata or any other properties of the already-closed file.

The Close File function can be in the form of a button placed alongside the Open File & Append to Current Document, Save & Save as buttons on the titlebar, &/or a command at the ☰ > Close File (CTRL-X) menu.

A 'Close File function is standard in editing-type programs -- or least it exists all such programs that I'd ever used -- & is thus familiar to users.

Tested: v1.8.0 (13 Nov 2021) portable, v1.7.1 (18 Mar 2021) portable from Github Releases

OS: Win 10 x64

Thanks !