Product settings - Content
The Content section is used to enter and edit the main product description that appears on the product page. The short description can be used in most RSS feeds, and might also appear in catalog listings, depending on theme.
Add the product description in Page Builder
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Open the product in edit mode.
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Scroll down and expand
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Enter a Short Description of the product and use the editor toolbar to format as needed.
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At the Description label, click Edit with Page Builder.
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Use the Page Builder content tools to edit the existing text and add other content (if needed).
Page Builder preview
When you expand the Content section for an existing product where there is content created with Page Builder, it displays a preview of the Description content as it would appear in the product page. Open the Page Builder workspace, where you can make any needed updates, by clicking Edit with Page Builder.
This content preview is enabled for the product and category forms by default. If performance suffers due to loading the preview, you can disable the preview in the Content Management configuration settings.
Add the product description in the editor
If Page Builder is disabled for your store, use the text editor to add the product content. Enter only plain ASCII characters into the text box. If pasting text from a word processor, save it first as a plain .TXT file to remove any invisible control characters. For more information, see Using the Editor.
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Open the product in edit mode.
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Scroll down and expand
img-md w-600 modal-image 
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Enter a Short Description of the product and format as needed.
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Enter the main product Description and use the editor toolbar to format as needed.
You can drag the lower-right corner to change the height of the text box.