I fill fields in a pdf with the following code.

private void populateFieldsWithData(Map<String, String> data, PDAcroForm acroForm, List<PDField> fields) throws IOException {
    data.forEach((key, value) -> {
        PDField field = acroForm.getField(key);
        acroForm.getFieldTree().iterator().forEachRemaining(pdField -> {
            if (pdField.getFullyQualifiedName().equals(key)) {
                try {
                    field.setValue(value);
                    field.setReadOnly(true);
                    fields.add(pdField);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
        });
    });
    acroForm.flatten();
}

The problem is that the text in the generated PDF is squashed/compressed.

I tried removing acroForm.flatten();. If I do and I click on the text in the generated PDF the text is adjusted and looks normal. But when I click elsewhere in the generated PDF the text goes back to beeing squashed/compressed.