Hello, I am an amateur about the PDF generation.

What I am doing now is that I want to render a page into PDF file and save it in database when I click a botton.

Source like this:

// botton action
public void pdfOutPut() {
    document dc = new document();
    String pdfPageURL = '/apex/PdfOutputLayout?id=' + pageId; 
    PageReference pageRef = new PageReference(pdfPageURL);

    dc.body = pageRef.getContent();
    dc.name = 'pdftest' + System.DateTime.now() + '.pdf';
    dc.folderid = folderId;
    insert dc;
}

Now the problem is when I want to render mutiple pages into one PDF, how can I do?

My consideration likes this:

public void pdfOutPut() {
    document dc = new document();
    for(int i = 0; i < list.size(); i++){
        String pdfPageURL = '/apex/PdfOutputLayout?id=' + pageId; 
        PageReference pageRef = new PageReference(pdfPageURL);
        dc.body += pageRef.getContent();
    }
    dc.name = 'pdftest' + System.DateTime.now() + '.pdf';
    dc.folderid = folderId;
    insert dc;
}

I use "pageRef.getContent()" to get the PDF's binary data so I guess I could add each PDF's binary data into one. But there is error seems like "+=" is not supported.

Does anyone could help me?

Or maybe there is another way to achieve it?

Thank you.