Please read the link I gave you. By hitting Enter twice at the end of a paragraph, you are adding complexity to the underlying code of your document.
You may want to read the entire series.
Basic Concepts of Microsoft Word - from Shauna Kelly
Reading that will save you time over the next couple of weeks.
I know that you reasonably want a program that works the way you want to work. With Word, you can only accomplish that by learning how Word is set up to deal with text. Without that understanding you are trying to get a ball of string up a hill by pushing on the string without rolling up the ball first.

I don't know. Word 2007 is ten years old and was never very good. I don't believe Microsoft is sending out updates.

Word 2010 is definitely an improvement. However, by default, it also puts space between paragraphs. You definitely do NOT want to get Word 2016 until it is a finished product, which, IMO, it is not. It is still better, for most purposes, than is Word 2007.

The methods that Jim gave you are much better than the ones you had been using. The methods you had used are in the nature of patches rather than repairs.