Searching "managing libraries in diptrace" in Google returns this link as the first result:
viewtopic.php?t=10937
That should get you started.

I think they are saying that if there is copper around the hole on either side of the substrate then the hole will get plated. They remove the .25mm ring of copper so that doesn't happen. Is there a specific reason that the holes need to be non-plated? I have created PCBs with thru-hole components t...

I don't know of a way to assign a hot key to a specific component. What I did is create a custom component library of my most used power, common, return, etc. symbols. I did the same for test points and net ports. One click to select the library and one more click to select the symbol. When I start ...

My installation of 4.3.0.1 works as expected.
Are you clicking the redraw button after changing the thickness?

RS-274X is the current Gerber format:
https://en.wikipedia.org/wiki/Gerber_format

In the Diptrace PCB Layout editor:
File->Export->Gerber...

Why I decided to test this on a Friday afternoon is beyond me. Expanding the design manager in PCB Layout all the way to the left does indeed leave one with no clear method to reset it. Uninstalling and then reinstalling DipTrace did not fix the issue. What I finally did was to uninstall DipTrace an...

In the PCB Layout program, with your PCB outline visible, select File->Renew Layout From Schematic->By Components...
Select the schematic and click "Open" in the file dialog.

That should import all of your parts to your layout. Next, arrange the components inside the outline.

If you haven't already, you might double check the pattern in the pattern editor and confirm that the origin cross-hairs are positioned in the center of the component.

The last time I was faced with this issue I believe that I created a custom component for one side of the mating pair and numbered the pins to match the other connector. I'm not aware of a cleaner way to do it.

The PDF text is selectable and searchable if TrueType fonts are used.

A previous thread on the topic:
viewtopic.php?f=8&t=14016&p=30450&hilit ... ble#p30450

and here:
viewtopic.php?f=3&t=11743