It is possible to apply heading styles to text and not have it appear in a Table of Contents or in the Navigation Pane.
If it shows up in the Navigation Pane, it will show up in a Table of Contents unless the Table of Contents does not include that heading level.
Problem #1: This is because Heading Styles (as well as others) are "Linked Styles" and can be applied to something less than a full paragraph. This article is a discussion of how this happens and what it looks like.
Problem #2: Nothing in a Table or TextBox will be reflected in the Navigation Pane.
Here is a screenshot from a sample document demonstrating Problem #1 Linked Styles used:
If you open the sample document, it is helpful to have both the Navigation Pane and Comments displayed.
Heading styles 1-3 have been applied six times in the document.
Only four of these show up in the Table of Contents and only one shows up in the Navigation Pane.
The one that shows up in the Navigation Pane does not even look like a heading style because it has direct formatting to appear as body text!
At the bottom of the Styles Pane, there is a checkbox to disable Linked styles. I usually keep that checked to avoid these problems.
Linked Styles at the Root of this Problem (and a solution for other problems I expect)
The sample document has multiple heading styles within one paragraph. Heading Styles are designed and intended to be paragraph styles. When they are used for an entire paragraph they predictably show up in Tables of Contents and the Navigation Pane. A Linked Style can be applied to selected text. When it is used this way it takes on the Character formatting from the style but not the paragraph attributes. It is these paragraph attributes that are keyed on by the Table of Contents and Navigation Pane.
I know that the designers at Microsoft thought there were good reasons to create Linked Styles. I do not care for them, at all. People who want to copy the formatting of a heading or other paragraph style can do so without needing this.
How to Apply a Heading Style So It Will Not Work in a TOC or on the Navigation Pane
Select text in a paragraph and apply the style. It will act as a character style for most purposes. It is that simple.
Unless you have non-printing formatting marks turned on to display, you may think you have the entire paragraph selected but Word will think otherwise because you did not select the (hidden) paragraph mark at the end of the paragraph. (This is more likely to happen if you have a space or punctuation before the paragraph mark.)
How to Apply a Heading Style So It Will Work in a TOC and Appear in the Navigation Pane
Click in the paragraph without selecting text and apply the style. (or)
Disable Linked Styles (command at the bottom of the Styles Pane in Windows versions) otherwise by using vba. (or)
Be very careful to select the entire paragraph. (This is not all that easy to do.)
Hyperlinks to Headings
If you attempt to insert a Hyperlink to a heading, only those that were applied to the entire paragraph will show up in the dialog.
Cross-References to Headings
If you attempt to insert a Cross-Reference to a heading, only those that were applied to the entire paragraph will show up in the dialog.
Notes about the Sample Document
Each instance of a Heading Style in the document has an accompanying Comment
When the style is applied to the beginning of a paragraph, that part shows up in the TOC but not in the Navigation Pane.
If the Comment is in the middle of the text that is in the Heading Style, it will cut off the part in the TOC at that point. This is not true if the style is applied to the entire paragraph. See the second and the fourth paragraphs for examples.
I do not know why any of the partial paragraphs appear in the TOC.
The same rules for when a Heading will appear in the Navigation Pane apply to the dialog boxes for insertion of Hyperlinks and Cross-References.
Because I've seen the problems that come from Direct Formatting, I deliberately formatted the only correctly applied Heading so that it looks like body text. This direct formatting has no effect on the Heading qualities of the paragraph style.
See also: Why use Microsoft Word’s built-in heading styles? by Shauna Kelly
Custom Headings That Do Not Show Up in the Navigation Pane
You need to assign an Outline level to a paragraph style for it to show up in the Navigation Pane.
You can have any style show up in the Table of Contents by changing the settings for the TOC field to include that style. This is not true of the Navigation Pane. It only shows paragraphs that have been assigned an Outline Level. The built-in heading styles already have this assigned.
(Assigning a level in a MultiLevel List does not assign an outline level but a numbering level.)
This is best done using the Outline view. Assign a level to the paragraph you want treated as a heading. Then update the style for that heading to match the formatting of that paragraph. See Outlining in Microsoft Word by Charles Kenyon.
Even when you get your custom heading style to show up in the Navigation Pane, you will not be able to right-click promote/demote custom styles while you can do this with the built-in heading styles. If you want to be able to do this, base your custom style on a built-in heading style.
Problem #2 - Headings in Tables or Textboxes
Here is a screenshot demonstrating this problem:
Headings inside Tables or Textboxes simply do not appear in the Navigation Pane. (Those in Tables will appear in the TOC, and in the dialog for creating cross-references.)
You may be able to use a Frame instead of a Table. Check it out. Frames and Textboxes in Microsoft Word
If you want to have headings that will not become bookmarks in a pdf conversion, on the other hand, put them in a Table or Textbox (without borders if you want). Control which headings show up as bookmarks in a pdf.
If you think this is a bad thing, use the Feedback mechanism to let Microsoft Developer's know.
Thanks to Rohn007 for his comments.
Thanks to Lisa Wilke-Thissen for her comments.
This article is locked. If you have a question, please post it separately, as a question, with a link to a sample document.