How to adjust the margin of PDF document

Recently, I downloaded several e-books, however, some of them's margin is too wide or too narrow, I need to zoom it every time when I open them use Adobe Acrobat XI.  So I decided to rebuild the PDF with an appropriate margin, finally, I made it. let's introduce how to do this. 

Some software you may need,  before doing the steps below.
1, Adobe Acrobat   --- do the major jobs; 
2, FreePic2Pdf        --- migrate bookmark;

The margin is too wide

 1, using Adobe Acrobat open the PDF,
 2, select the "Page Thumbnails" tab in the right column. 
 3, select the page you need adjust,  if multiple, you can press "shift" or "ctrl" to select the pages,
 4,  Right-click, and select "Crop pages";
 5, input the number in below place,  this means how much margins you want to remove.
 6, you can also apply "page range" to "all" , then all the pages will be cropped;  in here the problem is almost solved, but if you want to keep this setting permanently, you rebuild(print as) a new PDF.

















7, save and go back,  and then click "Print" in the "Files" tab, choose the printer "Adobe PDF", choose "all pages",  then "Print";
8, save as a new file, don't overwrite the original one, because you need to migrate the bookmark in further.
9,  using FreePic2Pdf to migrate the bookmark.  see steps in below screenshots;
ps, keep the "Page Zoom" as "Unchanged" ;

10, Then all mission completed,  you can also edit the metadata info of the e-book, if you need.

Ps, afterward I was thinking, whether we need the step 9 (using FreePic2Pdf migrate the bookmark).   Can we just using Adobe Acrobat like, 
    1, append(insect) the new printed PDF to the original file;  
    2, delete all the pages from the original file. 
then all original file's info & metadata can be kept.

The margin is too narrow.

Just like the steps in "margin too wide" case,

1, you need print the PDF,  applying the larger paper (A4, A3, etc.). 

2, go back to the steps above in "margin too wide" case.