What each option cleans
“Collapse repeated spaces” turns runs of spaces into one. “Trim each line” removes spaces at the start and end of lines. “Remove blank lines” deletes empty lines, “Turn tabs into spaces” replaces tab characters, and “Join into one line” removes line breaks entirely.
Fixing text copied from PDFs
PDFs store text as positioned lines, so copying often adds a line break at the end of every visual line. Join everything into one line first, then add paragraph breaks back where they belong.