There are a few online sources, but they don't check for proper citations and properly quoting sources. Just do a search for plagiarism checkers and see what's out there. FYI - at least one of them stores your paper in its system and has it available for future checkers. I don't know how I feel about that - with proper citations, etc., the work and the research is your property.
One program will tell you the ratio of the paper that comes from other sources, compared to the ratio of original writing. But it's up to you to make certain you cited things properly, paraphrased appropriately and referenced things to a good bibliography.
Kudos to you for caring enough to check if it's done the right way! I teach at a university, and far too many students do not take that seriously, and are not fluent in citations.