Using Preview to edit PDFs?

so, need add 5 blank pages @ end of pdf. select last page of pdf (on sidebar/thumbnail), , click edit -> insert blank page, page goes above last page! if have 3 pages on pdf, select thumbnail page number 3 , add new blank (hoping it'll number 4), ends going between page 2 , 3!
try move them around dragging thumbnails, can't! suggestions how this?

btw, can't add 5 blank pages after printing, must inside pdf beforehand

 

then drag them bottom of sidebar , delete blank page above not empty page.

here how can it:

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