How to merge transparent draw object into background with PDF?

I have created a PDF document with Writer. The front page of this document consists of a background picture, on top of which is a white semi-transparent “draw object” and on top of that again, the title.

When converting the document to PDF, the result is fine. When uploading the document to Google Documents however, it renders the draw object in black rather than white, which is undesirable.

I assumed the PDF conversion would “flatten” the layered front page into a single image. It seems the PDF however keeps the draw object separated from the background and that Google renders it black.

I don’t assume Google will do anything about this. So I would like to force the PDF conversion to merge this object down into the background, rather than using transparency. Is it possible to do that and how?

The PDF document on Google doc is available here.

In this case you need to create a merged image. I suggest that you create a cover in Impress or Draw with the empty semi-transparent rectangle where the title will fit.

Then use the Export As Images extension
to create a merged image that you can insert as the first page’s background.

Finally, add the title again in Writer.

Limit the PDF export to the PDF/A-1a feature set (File|Export as PDF → [x] PDF/A-1a). This milestone format doesn’t support transparency, so the content with transparency will be converted to an image.

Note that when text is covered by a transparent object, this means that the text will no longer be text, but an image, i.e. you cannot extract the text from it by selecting it.

And while the flattening gives satisfying results on “solid” areas, when the transparency is a gradient, then the results won’t look that good anymore…