Run formula over hundreds of prices in PDF

Some years ago, I had a similar task (with a few additional quirks, such as different pricing factors and different currencies).

In that case, I first ran an analysing JavaScript over the document, locating and reading out prices. At the same location, it placed a form field, and set the underlying price as its default value. Then, a second script ran through the fields and calculated the price to display. Finally, a copy of the document got flattened.

This was pretty straightforward.

JavaScript in Acrobat doesn't allow you to replace text on a page. The best you can do it add some type of annotation (form field, text comment, etc.) on top of existing text. JavaScript can search through a document for certain text and give you the coordinates on the page, which you can use when adding an annotation with JavaScript. Once you're done adding annotations, you can use JavaScript to flatten the pages, which converts the annotation text to regular page contents. So it's possible in a way, but getting precise placement of the new text could be tricky. It might be a good idea to redact the original prices so a user won't be able to discover them. You can do this via JavaScript using redaction annotations. This all assumes that the document doesn't have security restrictions that would prevent it, and you may also need permission from the supplier to alter their document.