Chuck,
In general, PDF is not editable, which was one of its good points in the past. This has since changed as programs will allow you to edit it and especially change it to a Word document and back.
PDFs are considered the easiest to work with for several reasons and many more I will probably forget:
1. It is a small document taking up less space Kb-wise than most other documents
2. It is called a portable document file for a reason. You can send it easily via email -- most email programs aren't set to block it -- and most everyone has a PDF reader which Adobe gives for free. Most people don't have .tiff readers lying around.
3. It is easily password protected.
4. They are very easy to merge.
5. They can be saved in or read in one column, two columns or more.
6. It is compatible across platforms: Linus, Mac, MS, Smart phones, etc.
7. Can be made from almost any document and retain formatting.
8. It can be encrypted and made so that no one can edit it.
9. Extremely difficult to infect with a virus.
10. Can be viewed within a web browser.
11. The PDF format was originally developed by Adobe for the U.S. Federal Government to store its legacy files. Currently, the U.S. Federal Government is still the largest user of PDF technology. Most individuals have encountered the PDF format when downloading electronic tax forms from the IRS. It is the only format which usually meets all legal requirements. Other formats such as .tiff, jpg, and .giff must be copied immediately to a CD or DVD so as not to leave a footprint.
12. When using a high end printer, the pdf file produces a superior image than other formats.
