I have a large writer document which contains many, many very short paragraphs. I would like to consolidate them into single paragraphs. I can manually delete the paragraph marks at the end of each line, but that method is very time consuming.
What do you mean? “very short paragraphs” are indeed “single paragraphs”. Do you want to make you whole document a single paragraph?
While editing your question, mention your OS and LO version.
Obviously you want to keep some of the paragraph breaks and to replace the others by something.
How can you make clear which paragraph breaks should persist?
Would it be acceptable for you to first remove all of them and then manually create anew the few you want to have?
Is this a kind of task which will occur repeatedly?
What “something” do you prefer? Hard linebreak? Space? Tab?
Are the paragraph breaks you want to delete accompanied by spaces? Always? Sometimes?