This is the problem:
# apt-cache pkg php-tcpdf/xenial [..snip..] Recommends: php5-gd, php5-mcrypt Suggests: php5-imagick
Should read:
Recommends: php7.0-gd | php5-gd, php7.0-mcrypt | php5-mcrypt Suggests: php-imagick | php5-imagick
This is the problem:
# apt-cache pkg php-tcpdf/xenial
[..snip..]
Recommends: php5-gd, php5-mcrypt
Suggests: php5-imagick
Should read:
Recommends: php7.0-gd | php5-gd, php7.0-mcrypt | php5-mcrypt
Suggests: php-imagick | php5-imagick