First off, by law everything you write is copyrighted the instant you put it into written words. However, that may not be enough protection though publishers are certainly not going to steal your works. Doing so would jeopardize their reputations and ability to do business. Besides which, the amount of money they could possibly get for your work is a drop in the bucket compared to what they can earn honestly. The only real reason you might need protection is to protect your work against some other individual. The following information will help you protect your work.
It should be of interest to writers that the "poor man's copyright" is not really acceptable in court and has not been since the 1960s when evidence rules were changed. By the 1970s, it had been completely chewed apart, so P&E offers this method only as an emotional salve for writers who need some form of protection and for its historical value. A better method would be to save a submission log and rejection letters as those are admissible in court should one have to protect one's writing from those rare individuals unscrupulous enough to steal.
This method also ignores the simpler and cheaper expedient of keeping a journal of submissions and rejection responses. As well, all of these tend to ignore the fact that the vast majority of publishers and agents are honest and will not steal your written work. This is because no one knows in advance which books will become best sellers. Also, if a publisher did steal a writer's manuscript and publish it, that writer would be sure to sound the alarm to other writers who would then avoid that publisher. Consequently, it makes better sense from their viewpoint to retain one's integrity and settle for an honest profit rather than only the profit from one book that might not sell well at all.
Letter templates for use when your work is used without permission. Templates created by Charles E. Petit, Esq. and published by Inklings. Used with permission.
It's also been noted by others that this service is best suited for large libraries and corporations and that payments usually go to the publishers. P&E has heard that little of such money goes to the authors. This is not verified as yet and is offered only as a caution to watch for.
Free Patents Online Database: This looks useful. It features over 100 gigabytes of data which includes the full text of US patents from number 4000000 to 6857132.