Because the float data type is not exact, when reading in a PDF file, making modifications, and then saving the PDF file, the PdfReal values are sometimes changed.
This can cause the modified PDF file to show forms in the wrong location when BBox and Matrix values are used.
The following BBox and Matrix values have caused me problems:
/Matrix [0.00168 0 0 0.001188 0 0]
/Length 65 0 R
/BBox [0 0 595.320007 841.919983]
/Resources 58 0 R
I have atteched the Patch File that covers my fix to this issue.