Preview document opens in small window

Just to add, rather than dragging the corners you can enter Full Screen mode by choosing Preview's View menu and select "Enter Full Screen", press "command shift F" or clicking the green grow button at the top left of the window.

Unless I managed to mess it up without knowing, cmd-shift-F is Slideshow in Preview.

Ctrl-shift-F is Full Screen.

I was trying to play with that earlier to add to my answer, but found myself in a Slideshow/Full Screen **** (but that's redundant).

That's what it's supposed to be but on three different Macs I have running Catalina 10.15.2 "ctrl shift F" doesn't do anything.

Which one is what it is supposed to be in Preview? I don't use any of the Full Screen garbage, so I don't know what it should be in Preview. I do know it should be cmd-shift-F just about everywhere else, though. In my Preview which I haven't altered in any way, cmd-shift-F is Slideshow.

Didn't mean to confuse you. What you said is correct…

"Unless I managed to mess it up without knowing, cmd-shift-F is Slideshow in Preview.

Ctrl-shift-F is Full Screen."

However, "Ctrl-shift-F" doesn't work on 4 of my Macs running Catalina 10.15.2.

There are preferences for the scale, but it will only open a window large enough to hold display all of the content.

I have my scale set to print size.

That's what it's supposed to be but on three different Macs I have running Catalina 10.15.2 "ctrl shift F" doesn't do anything.

Make that four Macs.

Yeah, the first time I read your comment, that's what I thought you were saying. Then, I read it again and was confused.