We apologize for the inconvenience caused, as per the description above, when you convert an 8 MB PDF file to Word, it converts only first page, Is that correct?
Try exporting the PDF file online using the URL https://cloud.acrobat.com/exportpdf on a different browser like Chrome or Firefox or Safari and see if this brings any difference.
If you are using the free desktop version of Adobe Reader, please sign out and sign back in with your current Adobe ID and password in Adobe Reader and check for any pending updates from help>check for updates. Reboot the machine and try converting the PDF file to Word and see if this brings any difference.
Have you tried converting another PDF file to Word? If it is specific to one PDF file, Is it possible to share the PDF file with us?