I found the same issue as https://issues.apache.org/jira/browse/PDFBOX-3109

When I processed the attached pdf(same as PDFBOX-3109's pdf), where the cropbox origin is (9,9),

with Pdfium.NET
{"text":"R", "x":280.2398, "y":724.3551}
{"text":"E", "x":284.8798, "y":724.3551}
{"text":"S", "x":288.5998, "y":724.2251}
{"text":"E", "x":293.2198, "y":724.3551}
{"text":"A", "x":296.8298, "y":724.3551}
{"text":"R", "x":301.5598, "y":724.3551}
{"text":"C", "x":306.2198, "y":724.2251}
{"text":"H", "x":310.8598, "y":724.3551}

With PDFBox
{"text":"R", "x":271.0398, "y":715.3551}
{"text":"E", "x":275.6798, "y":715.3551}
{"text":"S", "x":279.3798, "y":715.3551}
{"text":"E", "x":284.0198, "y":715.3551}
{"text":"A", "x":287.7198, "y":715.3551}
{"text":"R", "x":292.3599, "y":715.3551}
{"text":"C", "x":296.9999, "y":715.3551}
{"text":"H", "x":301.6399, "y":715.3551}

I think Pdfium.NET's API should return adjusted coordinates as same as PDFBox. 011939.pdf (80kb) downloaded 0 time(s).