LibreOffice Writer (or really Draw in this case) is not a PDF viewer. But it can edit PDFs. So it may be absolutely expected that it requires many resources to render/convert PDF with many schemes and graphics.
Use PDF viewer instead:
Atril (default in MATE);
Evince (default in GNOME);
Okular (default in KDE);
It looks like your File Manager is Files/Nautilus. The ability to open files by double clicking the file on the "Desktop" was removed from Files/Nautilus a few years ago. See THIS Gnome developers post explaining the change. You can still open files from within the "Desktop" FOLDER in Files just not on the Desktop itself.
I am trying to make a ...
This is a GUI way you can create and manage all your apps launchers, this utility is called "MenuLibre"
It is on Ubuntu Repos
sudo apt install menulibre
this app will appear under gnome apps once installed
Here is the Link to MenuLibre official Website
You should delete (if these files exist) following files:
sudo rm /usr/share/appimagekit/no_desktopintegration
Then invoke your app again and allow Etcher creating the .desktop file
Otherwise you can follow Kulfy's comment. A very simple and fast ...
I found the solution here:
Create the jupyter-lab.desktop:
Then write the code below (Replace <user> by your username) and save it:
Comment=JupyterLab is ...