locking an image in .docx

It helps to understand that Word is a word processing program, not a desktop publishing program. The concept of page is imposed for printing purposes only. Microsoft has gone to a great extent to display documents as they will print but pages are not elements of a Word document structure. This is an old but still accurate explanations by MVP Daiya Mitchell:

Word Doesn’t Know What a Page Is

You can position an object (image, shape, text box etc.) relative to the page edges. That is as "fixed" as you can define an object position in Word. However, as John and Bob have pointed out, you can't lock an object to a particular page, if that is what you are trying to do. The object will always appear on the page that contains the object anchor paragraph.

Unlike page layout programs like Publisher and InDesign, graphics in Word cannot be placed in a fixed position on the page. As the bot has explained, picture will always move with the text in which they are placed (for In-line positioning) or they will move with the text to which they are anchored (for floating graphics).

You can keep a graphic in the same position on the page by choosing Picture Format>Position>More Layout Options. On the Position tab, choose Absolute position in both the Horizontal and Vertical sections, and make the position relative to Page in both. The picture will stay in the same place on the page. If the text to which it is anchored moves to another page, the graphic will move as well, but will stay in the same position on the new page.

In Word, locking the anchor does not freeze the picture’s position on the page; it only prevents the anchor (the paragraph the picture is attached to) from moving when text is edited. The image can still move with its anchored paragraph or be dragged manually.

Key points and what to check:

1. Understand what the anchor does
   • For any wrapping option other than In Line with Text (e.g., Square, Tight, Through, Top and Bottom, Behind Text, In Front of Text), the picture is anchored to a specific paragraph.
   • Locking the anchor means that anchor stays with that paragraph; it does not stop the picture from moving relative to that paragraph.
   • Inline pictures do not use anchors at all and therefore cannot have their anchors locked.
2. If the picture is still “moving” when editing text
   • This usually means the paragraph the picture is anchored to is moving (for example, because text is inserted or deleted above it). The picture will follow that paragraph by design.
   • Locking the anchor will keep the picture on the same page as that paragraph, but it will not keep it at an absolute page coordinate if the layout reflows.
3. How to lock the anchor correctly
   • Select the picture.
   • Select the Layout Options icon next to the picture.
   • Choose a wrapping style other than In Line with Text.
   • Select See more (to open the full layout dialog) and then select Lock anchor.
   • Note: Anchor locking and positioning options are unavailable for inline images.
4. If a truly fixed position is needed
   • Word does not provide a “never move under any circumstances” lock for the visual position independent of layout. The closest behavior is:
     • Use a floating layout (e.g., Square wrap) and lock the anchor.
     • Avoid editing or reflowing the text above the anchored paragraph.
5. Verifying anchors
   • To see anchors and better understand what is moving:
     • Turn on Home > Show/Hide ¶ to show formatting marks and anchors, or
     • Go to File > Options > Display and select Object anchors.

References:

• Wrap text and move pictures in Word
• Move WordArt, a text box, or shape in Word
• Move, rotate, or group a picture, text box, or other object in Office for Mac
• Shape.LockAnchor Property
• ShapeRange.LockAnchor Property
• AnchorLock Class