How in Jaspersoft Server can I change 12.34 to 00000012.34 please?
JasperSoft Studio has the TEXT function which you can use in the "Text Field" like this...
Here the field QR is an integer, and the TEXT function converts it to a value with the "right number" of leading zeroes.
For example, if QR = 1037, then you'd get 001037 from the function.
If it's floating point you need, then the other answer works.
On the Text Field property, there's an entry called "Pattern"
There you can pretty much play with formats kind of like in Excel.