Generated pdf using Flying Saucer and Itext PdfReader Exception: com.itextpdf.text.exceptions.InvalidPdfException: PDF header signature not found

Question

I got the following Exception when I try to create and instance of PdfReader from a pdf file generated using flying saucer

Exception:

com.itextpdf.text.exceptions.InvalidPdfException: PDF header signature not found.

instance creation:

com.itextpdf.text.pdf.PdfReader reader = new com.itextpdf.text.pdf.PdfReader(new File(filesList.get(0)).getAbsolutePath());

seems the flying saucer does not generate a valid pdf that starts with %PDF, can you help me

flying saucer code

OutputStream os = new FileOutputStream(path);
ITextRenderer renderer = new ITextRenderer();
renderer.setDocumentFromString(html);
renderer.layout();
renderer.createPDF(os);
renderer.finishPDF();
os.close();