the title should explain my question. I tried the "Arbitrary Mask" with usually format i know from excel like 0 "x" and # "x" but it doesnt work so Acrobat seems to have a little bit different format system.
I just want a field where the user can enter a number and after going out of field the number should get displayed with an "x" behind. When editing the field the x should not be inside the form so just visual.
I don't know the length in numeric characters that you need to type in that field, so in the case that the you need a lengthy number separated by coma you can use a custom format script in the event target field like this:
var f = event.target;
if (!event.willCommit) event.value = "x"+ util.printf("%,0.0f", Number(event.target.value));
Using this expression answers your inquiry and also allows to use the value typed in that field with other dependent calculating fields in that form regardless of the "x" preface string value added to it.
He should have said condition of number length, but anyway I know this is old philosophy problem what is behind a number and what is in front of number but in this case I belive OP wants x after numbers and not before.