You can add blank pages to PDF.

Here’s the steps of how to add blank pages to PDF:

1. In the opened PDF file, click the ‘Preview’ icon in the upper left corner of the window to enter the PDF page preview mode.
2. Tap the ‘+’ icon at the end of the PDF page to add a blank page.
3. Select(long press/select icon) any page.
4. Tap any White ‘+’ icon to add a blank page.