As suggested by the commenter of the 1st comment, this is now Bug 142966
I think this is a bug. Asking here for confirmation, or other comments.
With 18.104.22.168, LibreOffice community, I have done the following:
- File → New → Text Document
- Format → Page Style…
- Text direction
The choice of text direction is the heart of my question. I will start with Left-to-right (horizontal). I do hope that the reader also has the choice of Right-to-Left (horizontal). I am not sure if a Right-to-left choice does not necessitate settings some Tools → Options… .
- Still with the Page Style settings, I set the Margins, each of Left, Right, Top and Bottom, to 0. Now pressing OK shows a warning about margins setting are out of print range. And it asks whether to apply these settings. I answered yes, to continue applying these settings.
- Next thing is to Insert → Image… . I inserted an image that is the size of the page. Which is A4 for me. To get an image that is the size of a page, one can separate the 1st page of a PDF file from the other pages of the file, and convert it to an image. JPEG format, in my case. And the PDF file I used is here.
- Insert → text box. Choose any size for it , as long as the whole box is not larger than the image. Now enter some text in the box, and click with the mouse any where outside the box.
And here is my point: if, in step 3, the text direction was Left-to-right
(horizontal), then after the click with the mouse the text of the text
box is visible. While with a direction of Right-to-left (horizontal), the text disappears.