pdftk debian can't generate fdf [error : Unable to find file]

I’m on debian 10. I was trying to use pdftk in order to use the generated_fdf command.
When I just

apt-get install pdftk

then

pdftk a.pdf generated_fdf output a.fdf

It output

    Error: Unable to find file.
    Error: Failed to open input PDF file:
        generated_fdf
    Errors encountered.  No output created.

I figured maybe the debian repo is not up to date so I decided to build it from the git repo
then I used :

java -jar /lib/pdftk/build/jar/pdftk.jar  a.pdf generate_fdf output a.fdf

it worked !!!
So in order to have the same code in dev (debian), testing (ubuntu) , prod (Windows) I decided to create a file here usr/bin/pdftk

#!/usr/bin/env sh
echo "pdftk_perso"
ls -l "$1"
whoami
java -jar /lib/pdftk/build/jar/pdftk.jar "$@"

the output is now

pdftk_perso
-rw-r--r-- 1 user user 208557 Sep 22 16:06 a.pdf
user
Error: Unable to find file.
Error: Failed to open input PDF file:
   generated_fdf
Errors encountered.  No output created.
Done.  Input errors, so no output created.

So again it’s not working as if it was trying to find the file named "generated_fdf"

FYI it works fine with windows and ubuntu