Is there a preference setting I can adjust so that new, or existing, files are opened at full size rather than in a reduced format requiring re-sizing?
With “full size”, do you mean Zoom 100% or document window maximized?
Zoom level is saved with each document. New window size may be operating system dependent.
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About LibreOffice and copy from there. Press edit below your question to add more information.
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If you mean the programs window size, i dont think that can be controlled by LO itself, but rather by the “window manager” of the operating system. As far as i can remember Windows should remember the Last Windows Size of a Program when it was closed … But my knowledge might be depricated here.