If you mean you want trim to remove blank lines, then no, Trim will not do that - it only removes whitespace at the ends of strings, not from the middle, and the Text property of a multiline TextBox returns a single string, which each line delimited by "\r\n" - so blank lines aren't seen by Trim.
Instead, try this:
string text = Clipboard.GetText();
string[] parts = text.Split(new string[] { "\r\n" }, StringSplitOptions.RemoveEmptyEntries);
tbOutData.Text = string.Join("\r\n", parts.Select(p => p.Trim()).Where(w => !string.IsNullOrWhiteSpace(w)));
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