How to remove white space from bottom of PDF itext

Question

I am trying to make a giant PDF that will contain all information on one page as there can be no breaks between the information in the document. it probably wont ever be printed so the size of the PDF is not an issue. Using Itext the only way I have found possible is to create a page that is 14400px long "or 5M in A4 pages, but this leaves a trailing white space if the document is shorter than expected (I dont ever see the document being longer than 14400px) this is my code so far

private void pdfSave() {
        float pageWidth = 200f;
        float pageHeight = 1440f;
        Rectangle pageSize = new Rectangle(pageWidth, pageHeight);
        Document mDoc =new Document(pageSize);
        String mFileName = new SimpleDateFormat("ddMMyyyy_HHmmss",
                Locale.getDefault()).format(System.currentTimeMillis());

        String mFilePath = Environment.getExternalStorageDirectory()+"/"+"pdf_viewer"+"/"+mFileName+".pdf";
        File dir = new File(mFilePath);
        if(!dir.exists()){
            dir.getParentFile().mkdir();
        }
        try{
            PdfWriter.getInstance(mDoc, new FileOutputStream(mFilePath));
            mDoc.setMargins(10,10,10,10);
            mDoc.open();

            String mText = mTextEt.getText().toString();


            mDoc.add(new Paragraph(mText,FontFactory.getFont(FontFactory.HELVETICA, 4, Font.BOLDITALIC)));
            mDoc.close(); 
        }

Edit: I have tried using a crop box and a second pass as stated in a comment, but my app crashes on this line if I debugging it

Rectangle rect = getOutputPageSize(pageSize, reader, i);