publishing workflow

Like James says, there's no one best way to do this. There are ways to make roundtripping through Word less painful. Of course, your Word export is never going to match your InDesign file, but it doesn't need to, does it? It just needs to be close enough for your colleague to find and edit the relevant sections, and then close enough structurally speaking for you to get the fresh content back into InDesign. 

But if you run this workflow on a regular basis (I did so for years, until the translation industry managed to produce tools that could work with IDML), you'll find yourself fixing a lot of post-edit formatting problems. If it's worth some money to make those problems go away, then I'd suggest that you spend that money! If your colleague is someone who would really rather be working in Word, then take a look at WordsFlow from Em Software. It's made for someone in your exact circumstances; it allows your collaborator to work in Word, and your total effort round-tripping between the two apps is, after you get it set up, very significantly reduced. 

But if your colleague isn't wedded to the Word platform, then yeah, InCopy is probably the most plausible tool. It doesn't cost you extra money, and it lets your colleague revise text with very little time investment from you. 

There are plenty of other solutions, but I imagine that they are all overkill for you. The master copy of the current manual - the absolutely final text - is in InDesign, right? You didn't e.g. export that manual content from some kind of CMS? If your InDesign file really is the One True Manual, then some time invested in teaching your colleague how to use InCopy would be time very well spent. 

In addition to what James has said, you might consider exporting the stories from InDesign to RTF rather than exp[orting to Word from PDF. I think you will find you get better accuracy.

There is no one optimal flow for this, especially starting from an existing ID doc. But I'd consider taking extra steps to make the update cycle easier for future revisions. 

If you pull the doc back to Word via PDF, take the time to clean up and organize it at that level, with clean and complete style usage, etc. Then try to maintain the 'integrity' of that draft version.

Then work out a polished import setup, with fully mapped style imports into ID.

Other than using InCopy, which has both good and bad points (many authors will balk at using a 'weird' tool), that's about the only workflow for editing and updating outside ID.

There are some rules about using Word in this kind of loop, too.... try to limit the number of different versions used, purge the file from time to time via export to RTF, urge users to use styles, etc.

Lots of expertise here on this topic. Ask away. 🙂