Hi,
It seems like that the external PDF indexing library was out of memory when the file was saved – I guess the file was either too large, or there are a lot of pages in the PDF, and the server could not handle them.
From the message, I am seeing that the server memory limit is set to 32M, which is concerningly low, as that might not be sufficient even for a plain WordPress installation. Indexing PDF or other document contents can be resource heavy, as the indexer needs to extract the file information, and load them to variables aka the memory.
I would highly recommend increasing the memory limit to at least 128M or rather 256M, if you have 10-15 plugins active. This article should help you out on how to do that.
That will immediately resolve the problem.