Ah, i jumped to the wrong conclusion: say $data->{customer_name}; works.

In my template i have:

 \TextField[name=Kundenname,width=\textfieldwidth,backgroundcolor=white, bordercolor={white}, value={[@-- $customer_name --@]}, readonly={true}]{\AdjustSize[l]{Kundenname:}}

And $customer_name expands to this weird noise:

Dprotect unhbox voidb@x group U@D 1ex{setbox z@ hbox {char 127}dimen@ -.45exadvance dimen@ ht z@ ontdimen 5ont dimen@ }accent 127ontdimen 5ont U@D aegroup mlich

I say \usepackage[utf8]{inputenc} and Umlauts get displayed correct except in something like [@-- $customer_name --@].

Update: I have no idea how to continue. Any further hints?

Best regards, Karl