PDFsam
Freemium
PDFsam Basic extremely useful tool for splitting and merging PDFs in a configuration that suits you.
jPdf Tweak
Open Source
jPDF Tweak is a Java Swing application that can combine, split, rotate, reorder, watermark, encrypt, sign, and otherwise tweak PDF files.
Adobe Acrobat DC
Commercial
Adobe Acrobat Reader DC is the industry standard for viewing, printing, signing and commenting on PDF documents.
Compare PDFTK Builder with alternatives
Compare PDFsam and PDFTK Builder and decide which is most suitable for you.
Compare Adobe Acrobat DC and PDFTK Builder and decide which is most suitable for you.
Compare jPdf Tweak and PDFTK Builder and decide which is most suitable for you.