Preparing for trial is a major job for all attorneys, mainly because of the all the paperwork that they have to sort through. Since most trial lawyers are very highly paid most law firms find somebody else to do most of this work so that the trial lawyers can focus on the actual trial. One of these areas is document review. Every document related to the case has to be reviewed; this can take up a lot of time so it is almost always outsourced.
Document review is when an attorney reviews all of the documents that are related to an upcoming case in order to determine their relevance and whether or not they are privileged. Basically it is where the attorney decides what he will and won't use at trial and what he will try to keep from being admitted as evidence. This can be a time consuming process so most firms outsource the work. They will find somebody else to review the documents so that they can get rid of the most obviously irrelevant of inadmissible ones. Ultimately the final decision on what goes into court will rest with the trial attorney.
In most cases document review is outsourced to other companies who employ their own lawyers to do the review. These are lawyers who specialize in this field of practice. In general the pay for these lawyers is a lot less than it is for a trial lawyer so it usually makes sense to use a service rather than having the trial lawyer do it. However if you need to have documents that are in a foreign language or which contain a lot of really technical information you will need to get a specialist who will likely be very expensive.
One thing that you have to be aware of when you are choosing a document review company is that a lot of them have started to send the work overseas to Asia to have lawyers there do the review. Obviously they do this to save money. This isn't necessarily bad since there are lots of very good lawyers in Asia, but you should be aware of it. There are times when it might become an issue having a lawyer whose only experience is with a different legal system doing the document review for you.
A lot of law firms these days have started to use computer software to do the document review for them. All they have to do is scan in the document and the software will determine its relevance and admissibility. This can be a good way to reduce the cost of document review but you are going to have to be careful. If you have an important case you may not want to leave important decisions like which documents to use up to a computer. Like all computer software it is useful but it is far from perfect.