The only way to modify a PDF in the way you want, cutting a single page in half, is to either use a PDF modification application such as Adobe Acrobat Professional and copy the content in the way you want, or to take screenshots, which are perfectly capable of creating print-quality work, provided you use them carefully
OLD INFORMATION, NOT VALID:
Most PDF editing applications offer this.
The cheapest way to do this is to install a PDF Printer (If you have Windows 8 or 10, there is one built-in called "Microsoft Print to PDF") and then printing the first page of the PDF to this PDF printer, and then the second page, creating two separate documents. Adding a second blank page would require more steps but is probably doable.
You can also use a tool such as PDF Split & Merge (PDF SAM) which has built-in split and merge functions and is quite simple to use and has a free version which I have personally used for some time. First you'd create a PDF of a blank page using a PDF Printer such as in the 1st option above. Then you use PDF SAM's split function to split your PDF into two pages. Then you'd use PDF SAM's merge function to add the blank page you created first to each of the 2 PDFs you created using the split function.
So the entire process would look like this:
- Open your document editor and create a new blank document.
- Print this document using the PDF printer on your computer. Save it as BlankPage.pdf.
- Open the 2-page PDF using PDF SAM and split this by individual pages into pg1.pdf and pg2.pdf.
- Open pg1.pdf in PDF SAM and use the merge function to add BlankPage.pdf as the second page.
- Repeat step 4 using pg2.pdf.