Yes, and you do not need to edit the theme files or create a child theme for it. Third-party widgets such as Google Programmable Search, chat tools or calendars come as a small snippet, and HubSpot lets you place it without touching the theme.
To show the widget in a specific spot on a page, open the page in the page editor, search for HTML in the Add panel, drag HubSpot's built-in HTML module into the section you want, paste the snippet and click Publish. The Embed module with Embed code works the same way.
If the snippet only needs to load (a script with no visible element), paste it under Settings > Advanced > Head HTML or Footer HTML of that page, or for the whole site under Settings > Content > Pages > Site Footer HTML.
Note that the theme's header search box uses HubSpot's own site search, which indexes the text of your pages and blog posts, not files uploaded to the File Manager. To make PDFs searchable, either list them by title on a page or use an external search engine such as Google Programmable Search.