I found this Dysprosium free software that can be used in this way
◦ Files should be batch separated by one dot as "xxxxx.abcdef.pdf"
◦ Each batch common tag sequence, that is, xxxx can be any length.
◦ Each file identifier in the batch, that is, abcdef can be of any length.
◦ Each merged file comes as xxxx_Batch.pdf with its common tag in the same directory.
◦ All files should be in the same directory, mixed with other file types or just PDF.
◦ Files in the list receive automatic dictionary sort. Any other sort is possible only manually in the GUI, using "Move Up" and "Move Down" buttons.
◦ Any PDF file that is not in form of xxxx.abcdef.pdf or the result of the previous operations should be removed manually using remove button or before the beginning from the batching directory.
Number of file and length of each could be thousands on condition of having enough hardware power to handle it.
It comes as a portable JAR file that is cross platform on all machines that run Java, Windows, Unix type including Linux, or MAC.