I have a bunch of text files, images and pdf files which I want to convert into a single pdf file. How do I do it?
Install Master pdf editor. It is a free tool that offers creating, merging and extracting pdf files. Check here for details about master pdf editor and installing it on ubuntu
If PDF is electronic paper, then pdftk is an electronic staple-remover, hole-punch, binder, secret-decoder-ring, and X-Ray-glasses. Pdftk is a simple tool for doing everyday things with PDF documents.
You can create pdf files from text or images with Libre Office then to stitch these togeter with other pdf files
It can also
and a lot more besides
More details here: Ubuntu Geek: List of PDF Editing tools