You need to use Google Chrome browser for this.
Google Chrome has a built in PDF reader.
If the PDF document is online then you need to access it using Google Chrome.
If the PDF document is on your PC then you need to type it's file location into Google Chrome's address bar.
When the document has opened in Chrome -
Left-click the printer icon at the right hand end of the top black bar.
A print options panel will open on the left.
Under "Pages" select the pages that you want to save.
Under "Destination" you want "Save as PDF" so if that's not what it says left-click on "Change".
A pop-up box will open headed "Select a destination".
Select "Save as PDF".
The box will close.
Now you will get a blue "Save" button at the top of the panel (instead of a "Print") button.
Left-click the "Save" button and you will get a "Save as" box where you can choose a location to save and name the selection of pages that you made.
Left-click the "Save" button at the bottom of the "Save as" box.