pdftk error when using checkbox on pdf form - pdftk

Question

When I use checkbox on pdf form, pdftk gives the following error and does not create output pdf.
Unhandled Java Exception:
Unhandled Java Exception:
java.lang.NullPointerException
at gnu.gcj.runtime.NameFinder.lookup(libgcj.so.12)
at java.lang.Throwable.getStackTrace(libgcj.so.12)
at java.lang.Throwable.stackTraceString(libgcj.so.12)
at java.lang.Throwable.printStackTrace(libgcj.so.12)
at java.lang.Throwable.printStackTrace(libgcj.so.12)

Answer 1

Today I am having a similar problem with Checkbox. And I also saw java.lang.NullPointerException error. After investigation, I found that it is because my fillable checkbox is using custom glyphicon ('X') as checkmark instead of default styling.
So after reading this answer https://stackoverflow.com/a/29034948/11898471, It does workout by getting rid of my custom checkbox glyphicon. Without seeing your code I don't know exactly how you may do it your way, but my situation is to flatten a client uploaded PDF form with custom checkbox. What I did, is to extract all form data and re-fill the form so they get rid of all custom checkbox markup. Something like:
$pdf = new Pdf($uploadedFile->getRealPath(), ['command' => env('PDFTK_PATH')]);
/* Extract form field to remove custom markup field that cannot be filled. Eg: custom checkbox icon */
$pdf2 = new Pdf($uploadedFile->getRealPath(), ['command' => env('PDFTK_PATH')]);
$data = $pdf2->getDataFields();
$data = (array) $data;
$fill_data = [];
foreach ($data as $field) {
if (isset($field['FieldValue'])) {
$fill_data[$field['FieldName']] = $field['FieldValue'];
}
}
/* Update form field */
$pdf->fillForm($fill_data)
->flatten()
->saveAs(storage_path('app/'.$flattenedFilename));