Is there posiblity to create report containing for example couple of invoices. I opening dataset for each invoice and for the last one I want to create one file with all of them. I know I can merge previev files(.ll) but there is any other way except modify dataset or marge files to do that?
Depending on your LL version and component usage you can use
LlPrintResetProjectState() (when working with the API) or the AutoMasterMode property of the component (.NET/VCL) to print a mail merge type project. Take a look at the Databinding 2 sample (for .NET or Delphi) that shows exactly how to print a serial invoice. For the API way, there’s some documentation in the programmer’s reference.
Besides, merging preview files works great and is also a good solution - which you already have discovered.