The easy and quick way to create pdf without Acrobat is: Pdfcreator
Pdfcreator is a free software that make pdf from any documents or design files that you will send to the Pdfcreator virtual printer.
To join multi pdf documents as a big one you can use the "Pdf Blender" software.

Openoffice and the pdf
You can use the famous and free OpenOffice suite.
Openoffice can easy export docs, spreadsheet, design file, presentation directly to the pdf format.
To export the open document you must simply use the: File -> Export as Pdf menu command

PDF Toolkit
Pdftk is free software (GPL).
Pdftk is a command-line tool for doing everyday things with PDF documents.
You can use Pdf Toolkit to:

* Merge PDF Documents
* Split PDF documents Pages into a New Document
* Decrypt Input as Necessary (Password Required)
* Encrypt Output as Desired
* Fill PDF Forms with FDF Data and/or Flatten Forms
* Apply a Background Watermark
* Report on PDF Metrics such as Metadata, Bookmarks, and Page Labels
* Update PDF Metadata
* Attach Files to PDF Pages or the PDF Document
* Unpack PDF Attachments
* Burst a PDF Document into Single Pages
* Uncompress and Re-Compress Page Streams
* Repair Corrupted PDF (Where Possible)

Pdftk does not require Acrobat, and it runs on Windows, Linux, Mac OS X, FreeBSD and Solaris.

There is a GUI for Pdftk