ios – Putting 2 existing pdf pages side by side (half size) in a new pdf without loosing resolution

In Swift, iOS, I have a pdf file with 2 pages.
I want to put the 2 side by side, on a new page.
For this, I have to scale initial pages half size and rotate .pi/2.

I managed to achieve this by converting pdf pages to UIImages and using a UIGraphicsImageRenderer. But with a critical loss of resolution.

I’ve tried improving the resolution by creating images as jpegData(withCompressionQuality: 1.0), to no avail.

So I would need to work directly on the pdf pages using CGPDFDocument format.
The code structure is as follows, to insert a single scaled page:

  if let _page = theCGPdfDocument.page(at: 1) {
    var _pageRect: CGRect = _page.getBoxRect(CGPDFBox.mediaBox)

    writeContextInDestination!.beginPage(mediaBox: &_pageRect)  

    // translate to compensate for the flip caused displacement  
    writeContextInDestination!.translateBy(x: _pageRect.size.width, y: _pageRect.size.height)  
    Scale (-1, -1) // rotate 180°  
    // add rotate as needed  
    writeContextInDestination!.scaleBy(x: -1, y: -1)  
    writeContextInDestination!.clip(to: _pageRect)  

    writeContextInDestination!.drawPDFPage(_page)  
    writeContextInDestination!.endPage()  // end the current page  
  }

writeContextInDestination!.closePDF()

But I do not succeed in inserting the drawing of the second page.
I’ve tried repeating lines 7 to 11 for a second page at line 13. No success.
What is the direction to look for ?