The best way to convert multiple OLM files into a single PST is to use an expert tool like PCinfotool OLM to PST converter. It can smoothly convert multiple files at the same time without losing any detail. They can perfectly convert batch or selective  OLM files, including emails and attachments, with complete accuracy. Also, this software is used for everyone, whether they are beginners or professionals. This software can easily use all versions of  Windows Operating systems.