Why text breaks when you copy it
PDFs store each line of a page separately, so copied text keeps a hard line break at the end of every line. Emails wrapped at a fixed width do the same. Removing line breaks with Keep paragraphs on joins those lines back into flowing sentences but leaves the blank line between paragraphs alone.
What each option does
Remove extra spaces turns runs of spaces into one. Trim each line drops spaces at the start and end of lines. Straighten curly quotes swaps typographic quotes and apostrophes for plain ones, which code, spreadsheets and some forms expect. Strip HTML tags keeps the words from pasted markup and turns entities like & back into characters. Remove emoji removes emoji, flags and pictographs while keeping © and ®.
Counts you can trust
Characters are counted the way people read them, so an accented letter or a single emoji counts as one. Word counts include numbers and contractions like "it's" as one word, which matches what most word processors show.