A resolution of 150 dpi is sufficient for your PDF files.
This programme is the most convenient possibility to create and edit PDF-files. In case you have access to this programme, it is most recommendable to use it.
Using free ware programmes like PdfCreator or freePDF, you can convert all kinds of documents to PDF-files via the printing function. A manual for the use of freePDF in detail is available on the webistes of the Technical University of Applied Studies Wildau (in German).