A: Since the trial is a formal proceeding, there are specific rules that the trial judge sets down that must be followed in his or her courtroom. Each judge has the discretion to control the trial in their own courtroom. There is always a court officer assigned to a particular courtroom to maintain order. That officer also facilitates handing exhibits to witnesses. I believe the rationale behind having a court officer take the documents or exhibits from the attorney and then hand them to the witness is so that there is no direct physical interaction with the witness being questioned.
However, there are times during a trial where an attorney will simply walk up to the witness who is being questioned and hand him or her document, with the court's permission. There is no hard and fast rule that requires the court officer to take the exhibit from the attorney, and then turn and hand it to the witness. It appears to be more a matter of the court's discretion in an effort to maintain control over the courtroom and to maintain the formality of the trial process.