An I/O error can mean several things including saving or opening a PDF document to flash or network drives with no space available or incorrect permissions. It can also be due to a corrupt file. 

Adobe Reader can also be displaying the error even though the file itself is readable by other tools. Follow the steps below to troubleshoot I/O errors displayed when opening PDF documents in Adobe Reader or Acrobat Pro:

  1. Save documents to local storage i.e. your hard drive before moving to a network drive or usb drive. This will ensure enough space is available to save the document and that the permissions on either the usb or network drive won't interfere with the file creation process.
  2. Split up large documents with more than 10-15 pages or ones with large amounts of text or images.
  3. Open documents in alternative PDF editors/readers such as Apple's Preview, Foxit Reader or even Google Chrome or Safari
  4. If the document opens in Preview or Foxit either Export or Save the document again using those tools or in the case of Foxit Reader print the document using the PDF Printer. Open the document again in Adobe Reader and it should display as usual.