We do not have implemented a limit, but there is normally a limit because of system or OS resources. If that large number of files does not work at once, try to join less files per document and then join these created files to one final file.
Our online PDF file joiner should not be used with a very high number of files, because it could take a lot of time to send all the files to the processing server. If you have to process a lot of files, then the PDF24 Creator is the better solution.
Have have also implemented special handling a high number of files. This is implemented in newer versions of the software.