Hrqls: All depends really there are reasons that people use PDF formats instead of the word, excel HTML etc etc

1) Security. You can set a document so it wont allow changes, additions or deletions (good for tenders and quotes etc)
2) Copyright: You can also set it so you cant select text, pictures etc and also choose whether the recipient can even print the document!!
3) Size: PDF can shrink word documents 20 fold, making for faster downloads etc