InDesign CS5.5 users can convert InDesign CS6–CC 2018 to CS5.5, via MarkzTools for InDesign plugins from Markzware, for file conversion:

As a leader in file conversion products development, Markzware supports Adobe InDesign CS5.5, InDesign CS6, InDesign CC, and other document production workflows. Every file conversion solution that Markzware develops undergoes quality assurance testing, to ensure a high-quality product.

Markzware offers an array of solutions, which include applications, file recovery, and InDesign plugins for your InDesign CS5.5 workflow. Markzware’s MarkzTools for InDesign CS5.5 is an InDesign plugin that can open higher InDesign versions in InDesign CS5.5.

Convert and publish InDesign CS5-CS6 files with the MarkzTools Bundle, to maximize the visibility of your existing InDesign CC version content! See how, in this MarkzTools demonstration video:

InDesign CS5.5 Users Convert InDesign CS6-CC 2018 to CS5.5: MarkzTools

Support in the MarkzTools for InDesign plugins (in the Markzware MarkzTools bundle) allows users to open InDesign files in prior versions. This includes opening InDesign CS6 through CC 2018 files in InDesign CS5.5.

Using MarkzTools for InDesign is simple. Just go to the MarkzTools menu, select “Convert InDesign Document”, and select the InDesign document that you wish to convert.

For decades, Markzware has been delivering substantial value to print, publishing, and graphic arts file users worldwide. Using MarkzTools to open InDesign CC files in earlier versions, DTP professionals will be able to post InDesign CS5-CS6 files, to inform or to collaborate.

… when you drop an InDesign CC 2015 or CC2017 INDD file onto, say, an InDesign CS6 running MarkzTools… No problem. The file will open right up for you! No missing plugin errors or other error dialogues from InDesign.
– pijnacker01, MarkzTools for InDesign user & reviewer
Source: https://steemit.com/indesign/@pijnacker01/indesign-version-woes-how-to-use-higher-version-indd-documents-in-lower-versions-of-the-application

Conversion software can offer major advantages for creative workflows. MarkzTools:
• saves money, since the InDesign CC version document does not have to be re-created.
• allows content access and dependable INDD file conversion, which can help to safeguard intellectual property.
• enables users of InDesign CS5-CS6 to modify newer versions of InDesign documents, including CC-CC 2018, through user-friendly menu options.
• lets you move InDesign content into an older INDD document version, without IDML.

MarkzTools for InDesign Feature for InDesign CS5.5 Users to
Convert InDesign CS6-CC 2018 to CS5.5:

Features that set Markzware MarkzTools apart includes many abilities:
1. The “Convert InDesign Document…” menu item supports file conversion of multiple versions of Adobe InDesign.
2. The Help menu displays:
• MarkzTools for InDesign version installed on your system.
• Online Manual Button to take you to a page where you can access Markzware product manuals.
• Support Website button to take you to Markzware’s Trouble Ticket form.
• OK button to close the MarkzTools Help window and take you back to InDesign.
3. Support for several languages, including English, French, and German.

File Conversion with MarkzTools for InDesign CS5.5 to
Convert InDesign CS6-CC 2018 to CS5.5:

Markzware‘s MarkzTools for InDesign maintains a high level of precision, as it converts data. From your InDesign CC version content, you can now create InDesign CS5, CS5.5, or CS6 documents and share your information with potential customers worldwide.

InDesign Versions Supported by Markzware’s MarkzTools for InDesign
MarkzTools for InDesign CS6 converts these InDesign versions to CS6:	• CC • CC 2014 • CC 2015 • CC 2017 • CC 2018
MarkzTools for InDesign CS5.5 converts these InDesign versions to CS5.5:	• CS6 • CC • CC 2014 • CC 2015 • CC 2017 • CC 2018
MarkzTools for InDesign CS5 converts these InDesign versions to CS5:	• CS5.5 • CS6 • CC • CC 2014 • CC 2015 • CC 2017 • CC 2018

Open later versions of InDesign files, within InDesign CS6, CS5.5. or CS5. MarkzTools for InDesign allows users to select options to customize the InDesign data conversion.

Neil Bennett, Editor of Digital Arts, MacWorld, reviews InDesign CS5.5:
… the creative tools are all rather innovative. If you’ve played with the Digital Publishing Suite beta, all of the interactive elements are still here – hyperlinks, slideshows, 360 Viewers, audio, panoramas, video, pan and zoom of images and Web View for placing live content such as Twitter and RSS feeds — but the Overlay Creator is now an Extension panel rather than a separate application. This is a great timesaver. The toolset isn’t going to make you a rival of app developers, but it does most of what you’ll need on a regular basis.
Source: https://www.macworld.co.uk/review/desktop-publishing/adobe-indesign-cs55-review-3281667/

MarkzTools features an easy-to-use InDesign conversion interface that makes it simple to open higher InDesign versions. What’s more, MarkzTools for InDesign can open InDesign CC or higher version files in a lower version, without a Creative Cloud subscription.

You can buy Markzware’s MarkzTools Bundle, to open InDesign CC in lower InDesign versions and to convert InDesign files to IDML.

The low-cost MarkzTools 12 Month Bundle Subscription provides 1 year’s use of MarkzTools2 and three MarkzTools for InDesign Mac plugins on a single computer. This includes all updates and upgrades during that term, starting on date of purchase. You can renew your subscription at the end of the term.

Software in Markzware’s MarkzTools Bundle includes:
• MarkzTools2
• MarkzTools for InDesign CS6 Mac
• MarkzTools for InDesign CS5.5 Mac
• MarkzTools for InDesign CS5 Mac
• MarkzTools and MarkzTools2 updates

For more information, please visit the MarkzTools2 page. Additional Markzware products are available via the Products page.

Did this InDesign plugin help you to open Adobe InDesign files in lower versions? Please feel free to subscribe to the Markzware Mailing List and to share your experience with Markzware on social media, via Twitter, Facebook, LinkedIn, Google+, etc.

InDesign CS5.5 Users Convert InDesign CS6-CC 2018 to CS5.5: MarkzTools