You add a paragraph and the picture moves. In Word, that can be normal behavior rather than a damaged file. A picture inserted in line behaves like a text character; a floating picture uses a different layout. Save a copy before changing a carefully arranged document.
Start with the picture’s role
For a figure that should follow its explanation, select it and open Layout Options, or Picture Format → Wrap Text in desktop Word for Windows. In Line with Text places it within a paragraph. It moves as surrounding text changes. Giving that figure its own paragraph is often easier to maintain than spacing it with repeated spaces.
For a small illustration with text alongside it, try Square wrapping in the copy. This is a floating layout: you can position the image and let text flow around it. Check the actual surrounding paragraph, not only the picture’s outline.
Movement and wrapping are different choices
If the image should retain its place on the page while nearby text is edited, inspect Fix Position on Page where available. That does not turn the entire document into a fixed canvas or remove the need to check later pagination.
If an alignment command is unavailable, Microsoft notes that In Line with Text can be the reason. Changing wrapping can enable other alignment choices, but also changes how the document flows. Choose that change for the layout you need, not merely to make a button available.
Make one small editing test
Add a short paragraph before the figure in your copy. Check where the image, explanation and following heading end up. Undo the test if unwanted, then save and reopen. If you will share a PDF, export and inspect the actual PDF, including the pages before and after the picture.
Word for the web has fewer wrapping controls and cannot move some floating pictures inserted in desktop Word. If that is your situation, open the copy in desktop Word to adjust the layout. Mac commands can differ from the Windows path above; use the corresponding platform section in Microsoft’s guide.