This annoying issue won't fire every time,but quite frequently.
PS.
I'm using following softwares:
directory opus 12 x64 pro 12.3 build 6183,Chinese version.
windows 10 x64 pro,Chinese version.
office 2016 x64 pro plus ,Chinese version.
That looks like something the Microsoft Word viewer is doing, not something Opus itself is doing, so I'd expect the same outcome in Explorer's viewer as well.
I also see this behaviour with Word Documents, both DOC and DOCX. This is on Windows 7 with Office 2016. As @rabbit says the previewer works fine in File Explorer.
If I stretch the viewer pane far enough left on a big enough display the preview eventually aligns correctly, however if I then close the viewer and reopen it immediately with the same stretched size the alignment is once again awry.
Having opened the viewer with a misaligned document, scrolling through the document with the mouse immediately realigns it correctly.
So resizing the viewer doesn't make it correct the layout, but scrolling it does...
On the face of it, that seems like a bug in the Word viewer. Scrolling is something it handles itself, without any real involvement on our side, so it must already and correctly know the rectangle we have told it to render into if it can display the document correctly when it starts scrolling, but is not using it properly until the scrolling happens.
Possibly we can fix things by sending it a fake scroll message or something after opening it.
I don't currently have Office 2016 so I'll need to get that and try to reproduce the problem and then try some ideas to create a workaround. (Reporting the problem to Microsoft is probably a waste of time.) If there are any other things that can help reproduce it (e.g. particular documents), please add them here.