In case the quick button for Forms on toolbar doesn't allow you to place selected form on web-page even you have the web-page unlocked, please do the following:
Add an advanced object to your document instead:

1     Click the Insert and Modify tab.
2     In the Insert section, click the Object button to open the menu and select Object.
3     In the Insert Object dialog box, click a tab to display an object group:
4     Click Forms to insert complete forms or individual fields and modules.
5     Select the item and make modifications as needed.
6     Click OK.