From The Document Foundation Wiki
Make the file as small as possible
In order to be most helpful, please make documents as small as possible, while still causing the bug. The simplest way of doing this is known as binary chopping.
- First, save a backup copy of the document.
- Open the document up in its native application (usually this is the application the document was created in):
- For .doc files, this will be Microsoft Word.
- For ODF files (those ending in .od*, where * is a letter) this will be LibreOffice.
- Then, repeatedly:
- Delete the top half of the document.
- Save it as a new document.
- Open the document in LibreOffice.
- Is the problem still there?
- If so, go back to the start of step 3.
- Otherwise, go back to the previous copy (or backup) and try step 3 again with the second half of the document.
- Once you have reduced the document down to the part that causes problems, (making sure to remove any confidential information), attach it to the bug report.