Unable to Adjust Size for pdf in Preview

Found it!

In Preview,

1. open the Inspector (Command-I)
2. Select the Crop and Rotate tab, whose icon looks like a small ruler. Change the units as required
3. Now use the select area tool and the corresponding (printed) dimensions will be shown in the Inspector.

As an alternative, you can also download Free Ruler, which displays a nice ruler on screen, though requires care in both setting the ruler DPI and ensuring that the PDF is viewed at 100% size.

I found out that it has to do, in my case, with embedding Types. after combinig them with preview or (I use a lot of chapters) the free tool PDF Merger Free (or in your case, reordering), it seems they swallow the whole fontbiblio (well, guess not, only feels like), so I drop them on the app PdfCompress (https://www.macupdate.com/app/mac/8823/pdfcompress), in which preferences I choosed, without touching the compression Size (just in the middle), as fonts base 14, or none (this is risky, don't do it without checking your whole Dok afterward, makes funny things if the fonts aren't standard). Hope this helps...