File engineering
Combining separate company files into a single file is what this phrase usually means, and in QuickBooks the work goes by the name file merge. You keep one file as the primary, the one that survives, and transactions from each secondary file are brought into it. Beforehand it helps to know which file is which, the QuickBooks version of each, and whether any list names repeat, since matching names are combined unless renamed first.
Related service: QuickBooks File Merge
Get a free evaluation