Terrible resolution after high res pdf insertion in word (Adobe plugin)

Dear all,

unfortunately I did not find any good solution so far and I need help to finish my dissertation. I have published something in a journal...they created a high resolution pdf file. Now I want to attach that pdf file at the very end of my word document (Word 2014; Adobe Acrobat reader installed). After inserting my pdf via "objects" --> adobe --> choose file....it looks terrible in quality.

I have tried to make tiff files out of the pdf file (1200 dpi) with Adobe....this worked, but it get incredible huge in file size.

I cannot understand why this Adobe Word plugin does not work well. It cannot be that a 4 mb pdf file has to be emerged to more than a 50 mb size tiff file. By the way you loose the "vektor" quality and get "pixel stuff" out of it. Microsoft said that this must be a problem of Adobe.

So my question:

How can I add a pdf file into word without loosing any quality?

Thank you in advance!