Can anyone tell me why this is happening? I can't see any differences or simularities in the images that explain such behavior.
These are documents created in Word and then saved as Adobe PDF.
What version of MS Word are your files being authored in? When you say 'saved as Adobe PDF', does that mean you choosing File > Save As within Word, then selecting 'PDF' from the 'Format' drop-down menu?
Yes, that's how I've converted the Word-document into pdf.
I thought that any editing/behindlying formatting would be "flattened", so that no content would behave as header or footer, even though it was so in the original document.
I've tried. It seems like the excact same job (similar icon). The content in header/footer is converted, but the images are still disappearing both by inserting pagenumber and updating.
I've tried using both "adding to existing" and "replacing existing". Either way the images disappear.
I've also tried changing the placement-preferences of the image in word, and saved as PDF again, but still the same error occurs.