the resolution problem when create single page pdf on word2013

It is the question on create pdf with acrobat DC or acrobat XI on word 2013 plug in. When create the 33 pages pdf on word 2013 with high res, It work fine on full set.

But when I create 1 pages out of 33 pages in high res queue, the 1 page pdf image turn to low res.

Then I test create 3 pages out of 33 pages in high res queue, the 3 pages pdf image also turn to low res.

It occur on Acrobat DC and Acrobat XI, why?