There has always been a dearth of good quality inexpensive tools to edit and annotate PDF documents. Most forms are today available as PDF files for download and I prefer to fill them out neatly on the computer, print and sign them. On Windows, PDF-XChange Viewer is a good tool for these tasks.
There is a newer version of this tool called PDF-XChange Editor that has more features and is paid-only software. However, the older PDF-XChange Viewer works fine for me and it is available free for academic use.
To add text to a PDF page: Tools > Comment And Markup Tools > Typewriter Tool > Default Style. Then click anywhere on the PDF page and start typing.
To move or edit text: single-click on the text to select the box of text, double-click to edit it.
To change the formatting of the text: right-click in edit mode and choose Show/Hide Text Formatting Toolbar. The toolbar appears at the top. Change the font or size and click the Make Default button to make this the default style.
Tried with: PDF-XChange Viewer 2.5 and Windows 7 x64