Unicode characters can be inserted with

Ctrl+x 8 " a => ä
Ctrl+x 8 " A => Ä
Ctrl+x 8 " s => ß

See list of characters generated this way

Ctrl+x 8 Ctrl+h

To avoid repeating 'Ctrl+x 8' too often

Alt+x set-input-method latin-2-prefix

Convert file encoding from Dos to Unix

C-x RET f undecided-unix