A 100 MB PDF for an A3 photo usually means the export settings are much higher than needed, especially if you chose no compression. So yes, it can be normal with those settings—but it’s probably excessive.

For high-quality color printing, 300 dpi at final print size is generally sufficient. An A3 image at 300 dpi is roughly a 15 MP file. If the PDF was exported at something like 600 dpi, 1200 dpi, or even 2400 dpi, file size rises very quickly.

Using some compression in the PDF is also normal. A high-quality JPEG setting in the PDF export often keeps visual quality while dramatically reducing file size. Check the result at 100% on screen for visible artifacts.

So:

• 100 MB is not inherently “wrong,” but it’s larger than necessary for most A3 photo prints.
• Re-export at final A3 size around 300 dpi.
• Use high-quality JPEG compression unless your printer specifically says otherwise.
• Large files may still print fine, but they can be slower to upload, process, or RIP at the print lab.

If in doubt, ask the printer for their preferred PDF export preset or required resolution.