Export pdf is a Document Cloud service which you can use online via- https://cloud.acrobat.com/exportpdf
Document Cloud services allow you to upload and convert files that are up to 100 MB. Document Cloud Help | File size limitations
It doesn't have limit to the number of files, but it does have the total file size limitation.
If your file size exceeds the limit of 100MB then that might be causing problem in this case.
Hope this answers your query.
Thank you for your response. Is there anyway we can upgrade the file size
limit for converting PDFs? Also, is it possible to download more than 50
converted files at a time?
Sorry to say, with the document cloud services there isn't a way you can upgrade the storage size.
When you convert a pdf to word the conversion goes one by one so you download the converted file one at a time but if you still want to downloading more than 50 converted files, so can do that but that might cause interruption in network and slow network connection.