The first is to use Adobe Acrobat DC, open the file and click the organization page.
At this point, the pages in the pdf file will be displayed as thumbnails. We click Insert and select a blank page.
Just set some properties for inserting blank pages.
The second method is to use the xunjiePDF editor, which is relatively simple.
After opening the file, click the document button, and then select the page thumbnail.
At this point, a thumbnail box will pop up on the left side of the interface. We just need to right-click the thumbnail page in the thumbnail and select Insert Page-Insert Blank Page. In this way, a blank page will appear at the back of this page.