which version of PDF for general use/distribution?

I do a lot of quick-and-dirty PDF creation of long documents (100+ pages), for distribution to cli开发者_高级运维ents; my clients are often individuals, but sometimes corporate managers at banks and insurance companies.

Acrobat Pro allows you to save in many versions of PDF, from Acrobat 4 - Acrobat 10. Which should I use, as a general rule?

I don't often use advanced features in my documents: usually pictures and text. Since I send via email, I want the best compression possible... my documents often have lots of images. However, since my clients are banks and such, not cutting-edge technologists, I don't think they have the most recent Acrobat/PDF reader installed.

What is the best PDF version, as a compromise between document compression and widespread adoption?

I recommend PDF 1.4 - Acrobat 5. PDF/A-1 (PDF for archiving) standard is also based on PDF 1.4.