LibreOffice – Open File from Terminal

See the following images to know how to create a text-box.

Click the icon with an A with a vertical bar next to it:

Type whatever code you want to put in the box and then right-click on the border on the box. Select Line from the menu.

Select the style you want for the box's border and click ok.

libreoffice comes with an option to convert an odt file to plain text, which then can be edited with your preferred command-line text editor and (if wanted) converted back to odt.

1. Convert document.odt:

   libreoffice --convert-to txt document.odt
   

2. Edit the file with your preferred text editor, e.g.:

   gedit document.txt
   nano document.txt
   vim document.txt
   

3. Convert it back. The --convert-to takes a filename extension as an argument, but you may also specify a filename suffix to prevent libreoffice from overwriting the original file (which it does without asking!):

   libreoffice --convert-to _new.odt document.txt
   

For the conversion there's also odt2txt, I'd just try both and compare the results.

If you're using vim you can configure it to automatically do the conversion for you in the background, see: Is it possible to easily work with .odt, .doc, .docx, .rtf, and other non-plain-text formats in Vim? The answer there uses odt2txt for the conversion, but it should be possible with libreoffice --convert-to as well.