Ctrl+D for ending terminal line input

If I do

$cat > file.txt
text<Ctrl+D><Ctrl+D>

Question1: If I don't press enter, why do I have to press Ctrl+D twice?

If I do

$cat > file.txt
pa bam pshhh<Ctrl+Z>
[2]+  Stopped         cat > file.txt
$cat file.txt
$cat > file.txt
pa bam pshhh
<Ctrl+Z>
[2]+  Stopped         cat > file.txt
$cat file.txt
pa bam pshhh

Why is the second time the file with 1 line?