Draw the contents of a PDF file to the canvas

My Android app is using PdfDocument to programmatically generate multipage PDF files:

public byte[] buildPDF() {
    int pageWidth = Math.round(8.5f * 72f);
    int pageHeight = Math.round(11.0f * 72f);
    int margin = Math.round(.5f * 72f);
    int fontSize = 12;

    TextPaint textPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
    textPaint.setColor(Color.BLACK);
    textPaint.setTextSize(fontSize);
    textPaint.setTypeface(Typeface.DEFAULT_BOLD);

    PdfDocument document = new PdfDocument();
    PdfDocument.Page page = null;
    Canvas canvas = null;

    for (int i=0; i<10; i++) {
        PdfDocument.PageInfo pageInfo = new PdfDocument.PageInfo.Builder(pageWidth, pageHeight, document.getPages().size()).create();
        page = document.startPage(pageInfo);
        canvas = page.getCanvas();

        String content = "Content for page " + (i + 1);
        canvas.drawText(content, margin, margin + fontSize, textPaint);
        document.finishPage(page);
    }

    byte[] output = new byte[0];
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    try {
        document.writeTo(outputStream);
    } catch (Exception e) {
        Log.d("buildPDF", "error writing PDF output");
        return output;
    }
    output = outputStream.toByteArray();
    document.close();

    return output;
}

In some cases, I want to put an existing PDF file on my local device into this series of pages. The easiest workflow is to somehow open the PDF file as data and then write it to the canvas. Is there any way in the Android SDK to do this?

It's easy to use CGPDFDocumentRefand in iOS CGContextDrawPDFPage, but I haven't found an Android equivalent.

If there is no built-in method, the package in Apache PDFBox seems to work fine. However, I need the data in memory as described above, so I figured this would require writing the resulting data to a temp file, performing an operation on the temp file, and then reading the data back into memory.multipdf