pdftk is a very useful and powerful pdf-toolkit. It is available for Ubuntu with the package pdftk. Here are some practical example if its usage.

• Merge Two or More PDFs into a New Document:

  pdftk 1.pdf 2.pdf 3.pdf cat output 123.pdf 

• or (Using Handles):

  pdftk A=1.pdf B=2.pdf cat A B output 12.pdf 

• or (Using Wildcards):

  pdftk *.pdf cat output combined.pdf 

• Split Select Pages from Multiple PDFs into a New Document:

  pdftk A=one.pdf B=two.pdf cat A1-7 B1-5 A8 output combined.pdf 

• Rotate the First Page of a PDF to 90 Degrees Clockwise:

  pdftk in.pdf cat 1E 2-end output out.pdf 

• Rotate an Entire PDF Document's Pages to 180 Degrees:

  pdftk in.pdf cat 1-endS output out.pdf 

• Encrypt a PDF using 128-Bit Strength (the Default) and Withhold All Permissions (the Default):

  pdftk mydoc.pdf output mydoc.128.pdf owner_pw foopass 

• Same as Above, Except a Password is Required to Open the PDF:

  pdftk mydoc.pdf output mydoc.128.pdf owner_pw foo user_pw baz 

• Same as Above, Except Printing is Allowed (after the PDF is Open):

  pdftk mydoc.pdf output mydoc.128.pdf owner_pw foo user_pw baz allow printing 

• Decrypt a PDF:

  pdftk secured.pdf input_pw foopass output unsecured.pdf 

• Join Two Files, One of Which is Encrypted (the Output is Not Encrypted):

  pdftk A=secured.pdf mydoc.pdf input_pw A=foopass cat output combined.pdf 

• Uncompress PDF Page Streams for Editing the PDF Code in a Text Editor:

  pdftk mydoc.pdf output mydoc.clear.pdf uncompress 

• Repair a PDF's Corrupted XREF Table and Stream Lengths (If Possible):

  pdftk broken.pdf output fixed.pdf 

• Burst a Single PDF Document into Single Pages and Report its Data to doc_data.txt:

  pdftk mydoc.pdf burst 

• Report on PDF Document Metadata, Bookmarks and Page Labels:

  pdftk mydoc.pdf dump_data output report.txt