depends on what software you have. I would recommend downloading inkscape (incredible free open source drawing program). it can edit pdfs very well (it is a vector, not a pixel editor, which makes it well suited for the job) and it has alot of online tutorials to help you get starter. but remember it is a very advanced and powerful program, so dont expect to be able to figure it out in the first day (or week. or month (jk)).
other then that, there is adobe illustrator, but that is crazy expensive. also, this is a bit simple then inkscape so you might want to try it out.
PDF is a very interesting format. Instead of saving ANY file into it's original format, you save it to a PDF so that the layout - fonts - images - margins don't change at all. Sometimes between versions of software a normal document (say a Microsoft Word file) will change layout depending on certain circumstances. But if you save that document to a PDF file - while you can't edit it directly, you can still be sure it is as the original publisher intended.
What you are looking for is any program you can design a plan in - and then save that to a PDF.
Personally I use AutoCAD 2012 for my plans and drawings, and I have the option to export to one or several PDF files. If you want, you could send me a photo of a detailed sketch and I could CAD it out for you and export it to PDF.
There's open office too. But although it creates pdf files I haven't used it yet. I'd go the free route first. I know folks that have crawled into Autocad and I haven't seen em since. They won't answer the phone. just a powerful program that is.