I use Open Office Writer and I'm roughly 20,000+ words into my novel. Thing is I'm becoming paranoid about the way I have my text formatted, and keep convincing myself that should I send it to anyone, all they'll receive is an unformatted wall of text. Is there anything I need to be doing to ensure the formatting I'm using (indents for new lines, etc) will be received by someone else (who may be using a different program to view it) correctly formatted?
That depends on the program they use. Since Word is such an well-used program in pretty much any industry where any kind of text is written most programs can open .doc files. However, unless the person(s) you are sending the file to need to be able to edit it (or are agents/publishers) the best alternative is probably to use .pdf. PDF is universal, so your document should look identical to everyone who views it. It should also not be affected by any of the incompatibility issues that may occur when opening .doc in OO/exporting .doc from OO.
Publishers will usually specify what format they want submissions in - in my experience it's .doc, .docx, sometimes .rtf or .pdf. I don't know about Open Office but Libre Office (which I use; it's also free) is able to save in those formats. I'd see if Open Office can do that or get Libre, and save your documents in .doc or what have you to see if the formatting is carried over, and fix what needs to be fixed. You also might want to look at Shunn's proper manuscript format and start conforming to that if you don't already, because while deviations aren't going to get an amazing story rejected (well not unless they're pretty severe), it's usually best to stick to it and forego any fancy formatting.
OpenOffice is an "sister" to LibreOffice. At first only OpenOffice existed, then LibreOffice was branched off from it at some point (but OO is still being updated). So the two programs have a lot of similarities.
Thankfully I format virtually identical to this, aside from the headers and line spacing - which are both easily fixed. So if I save it in .doc and email it to someone who has Word and ask them to open it. That'll prove whether or not the formatting holds?
Somewhat worryingly, saving in .doc throws up a warning that formatting may be lost when opened in Word. Now what??
Send it to someone and see if formatting is lost. You can try the rtf or pdf route, but most agents/publishers I'm familiar with want doc or docx. I think you need to try to give them what they want.
OpenOffice and LibreOffice always give that warning. The vast majority of the time it is fine. I've gone back and forth with complicated formatting with no trouble. Simple manuscript format should be preserved.
From my experience stuff like text style (italic, bold, etc.), as well as indents, line spacing, margins, etc. (i.e. the simple formatting used in manuscripts) should be exported without faults. More advanced stuff like diagrams, graphs, equations, and possibly tables are more likely to fail.
Thanks all. My recipient tested it in Word and all is fine. I have them trying it in any other WP they might have, too.
Word's really the one you have to worry about. @Wreybies doesn't want to hear it, but... I think @Wreybies is on vacation, so let me tell you while he's away! Word is the industry standard. That doesn't mean it's better than anything else, but it's what's used in the industry. I'd honestly be a bit wary of an agent or editor who wasn't using it.