Hi,
The memory limit is still 32M according to the error message, it did not change. Make sure that the correct php.ini file was changed, and that the apache or the php-fpm service was restarted on the server.
There is no file or any other limitation in the plugin. It could be the file size, but it is more likely the very low memory. PDF indexing is a very costly operation in terms of CPU and memory, that is why it is done individually during indexing or during saving the files.