PDFmod is a simple tool with GUI to modify your pdf documents.
You can:
1) Rearrange pages of a pdf file
2) Combine two pdf files
3) Delete pages from pdf file
4) Rotate required pages
For more advanced exhaustive set of tools look at PDFtk (PDF tool kit).
PDFedit is an advanced editor which allows you to edit text in pdf files.
All the above softwares can be installed through package managers.
