Alex,
A conversion table operates on tags, not on formatting properties. You can have a format named Bold that does not set the text to bold. You can have text that is bold but does not have an identifying tag. In your case, it is probably straightforward to tag the bold content in a way that is compatible with a conversion table.
First, some background. A FrameMaker character format is a set of properties (weight, angle, font family, font size, etc.) which may or may not include a character tag (or name for that set of properties). Furthermore, a document has a character catalog, in which you can store named sets of character properties. Such a format need not define values for all the possible font properties. Setting any property to As Is means that you can apply the format to text and will only change the properties defined in the format. Once you've defined a character format, you can easily apply it to selected text. Furthermore, you can change any of the properties associated with text to override an applied character format from the catalog.
Try the following. Create a new document and type some text. Select some but not all of the text. Use the Format > Characters > Character Designer command to bring up the Character Designer. If you are using FM 2017, notice that the Style box at the top of the designer is empty (if you are using an earlier version, some of the details I mention will vary slightly, but I suspect you will be able to follow these directions nonetheless). Select Bold from the Weight pull-down menu and click Apply. The text is now bold. However, if you look at the left of the status bar at the bottom of the document window, there is no indication that a character tag was applied. Furthermore, the Style box is still empty.
Now type some text in the Style box, say Test1. Click the Create Style button at the bottom. Look at the status bar. It now indicates f: Test1 to show that a character format named Test1 has been applied to the current content. Click outside the bold area in your text. The status bar no longer shows the character format and the Style box once again is empty. In the lower-left corner of the Designer, FM 2017 displays the gear icon widely used by a variety of software to edit settings. If you hover over this icon, FM displays Commands to indicate that it is a Commands button. Click on the icon to invoke the Commands button. One of the commands is Set Window to As Is. Select this command. Now type Test2 in the Style box and Click Create Style. You now have made two new entries in your Character Catalog. There are various ways to apply them. One of them is to type the desired tag (Test1 or Test2) in the Style box, or to select the tag from the pull-down menu at the right edge of the Style box. Once the tag is displayed in the box, click Apply.
The difference between Test1 and Test2 is that Test2 only applies bold. Test1 applies all the properties that were current when you created it. So if you use different sizes or font families in different contexts, applying Test1 may well change the size or family as well as the weight while applying Test2 changes only the weight.
In my earlier message, I mentioned the Create and Apply Formats command, which is on the File > Utilities menu. This command creates new formats in the appropriate catalog as needed so that all paragraphs and text ranges within them are tagged. This command is helpful in structuring documents in which formatting differences are not always tagged. However, there are often numerous variations of formats that differ in properties that are not relevant to your project. Create and Apply Formats would give each of them a unique name and accounting for all such names can greatly complicate a conversion table.
If identifying bold text is the only case in which you need a new format, you can use a different technique. Open one of your Word documents. Create a character format called Bold that is like Test2 in your earlier test document. Make sure to store the format in the Catalog by clicking the Create Style button. Apply this format to one instance of bold text. Use Edit > Copy Special > Character Format to store the result on the clipboard.
Next, bring up the Find/Change pod. From the pull-down menu at the right edge of the Find box at the top of the bod, choose Character Format. The Find Character Format dialog box appears. Press F8 to set all fields to As Is. Change Weight to Bold. Clicking Find will now find occurrences of bold text. In the Change field, select By Pasting. You can now click Find followed by Change to apply Bold to text that was bold. Change All will change all bolded text in the document. You can copy your new Character Catalog to another document with File > Import > Formats. If you have FM versions of all the Word files in an FM book, you can import the Character Catalog into all of them in one operation. You can then do a global Find/Change in the book to modify all files at once.
Hope this helps.
--Lynne