Sometimes when you scan a document in your scanner into a PDF file, the orientation is all wrong. Usually you can re-scan the same document with correct orientation, but sometimes you no longer have the original document anymore. In those cases, the only solution is to rotate the existing PDF file. The open source program called FreePDF allows you to rotate and merge PDF files together easily.
You can download the FreePDF application from its sourceForge website. The download is available in form of an installer. After the installation, you can run it from its desktop shortcut if it does not run automatically by itself. In the FreePDF window, you have to start by adding PDF files on which you want to work on. You can add PDF files by clicking on the Add Files button.
Once a PDF file has been added, you can select it from the list and then click on different buttons on the top to rotate it 90 degrees clockwise, 180 degrees or 90 degrees anti-clockwise. You can do this for all the added PDF files one-by-one. After this is done, you can click on the Rotate button to finalize the rotation. This would overwrite the PDF files with their new rotated versions. However, if you want to merge all the added files into a single PDF file, then you have to click on the Merge button and choose a new PDF file name for the new merged file.
FreePDF has a very simple and easy to use interface that allows you to permanently rotate PDF files and merge two or more PDF files together. This feature is not present in popular PDF applications like Adobe PDF viewer and can come handy when you have nothing but the PDF files to work on.
You can download the FreePDF software from http://sourceforge.net/.