PDF Tools & Editors

PDF Annotator

[1] online/free/for signatures https://www.pdfescape.com/

PDF Tools 

$sudo apt-get install pdftk

$pdftk A.pdf cat 1-9 26-end output B.pdf # keep pages 1-9 and 26-end of the original file

$pdftk file1.pdf file2.pdf file3.pdf cat output newfile.pdf #join

$convert file1.pdf file2.pdf file3.pdf output.pdf #reduce resolution

$sudo apt-get install pdfmod #remove pages, works with A4

$sudo apt-get install pdfshuffler #remove pages, works with beamer too

PDF Editors

[1] Master PDF Editor http://code-industry.net/
[2] Fonst http://linuxg.net/how-to-install-master-pdf-editor-1-9-on-ubuntu-linux-mint-debian-fedora-opensuse-and-many-other-linux-systems/

[3] xournal, is possible add notes and free text, and [3] have other edition tools.
http://kuboosoft.blogspot.com/2012/07/5-editores-de-pdf-para-linux.html  
 
[4] Extract images from PDF online
http://pdfaid.com/ExtractImages.aspx

[5] How to extract part https://askubuntu.com/questions/221962/how-can-i-extract-a-page-range-a-part-of-a-pdf