If a TAdvRichEditor is set to read only, it does not allow the keystroke used to copy a selection of the text (Ctrl C), however the right click menu copy does appear to work. It appears that the TAdvRichEditor.KeyDownN function is exiting too early and not allowing the keystroke to process.
I retested it with the latest version of TMS VCL UI Pack v10.5.3.0 and I cannot reproduce this.
This is also using the latest VCL UI Pack from March 10th, but the control reports 18.104.22.168
In my test, I had two TAdvRichEditors on the screen, one read only and preloaded with some text. Opened wordpad and first copied different text into the clipboard. I then went to the read only editor selected some text and typed CTRL-C to copy to the clipboard, navigated to the non-read only editor and pasted...it would paste the wordpad text. Returning to the read only editor and selecting and using the right click copy and then pasting works as expected.
I tracked the problem down to the keyboard handler TAdvRichEditor.KeyDownN in AdvRichEditor.pas. The first line is :
if ReadOnly then
and the dispatching for CTRL characters (which includes VK_C) are near the end of that routine.
We could now see the issue.
It is traced & solved now and the next release will have this fixed.