Could be backlinks from sites like Scribd or could mean article marketing which is writing an article for your keyword and posting it on article directories.
If it is writing documents, then that should be writing articles to be submitted to different article directories. You can actually use that technique to improve your search ranking. Before writing articles, you have to look for an interesting topic first, then do a research on that topic and analyse it carefully. After that, write your articles well and avoid grammatical errors; that will make the readers really believe in your credibility. Also, do not copy from an article you that you found from another article directory because Google filters duplicate contents and it won't appear in search engines.
We can use a document in lots of ways for better search engine rankings like: 1. Submit on ezine publishing on websites 2. Sharing it on document sharing websites 3. Submit it as guest post on other blogs 4. Publish it on your own blog 5. use it as a press release etc
I think writing documents means creating content for high SERP rankings. If you are really planning to adopt this strategy, make sure you are not using copied content or low quality content... only then you will be able to get good rankings. As, after Panda update poor quality content is plummet by Google.