Resize before you insert: not after
Most documents display images at a few inches wide, but phone cameras save them at poster size (4000+ pixels wide). Resizing them to the actual display width cuts pixels and size proportionally.
You do not need exact math: aim for ~150 DPI at the printed size. An A4 page is about 8 inches wide. 1200 pixels wide is more than enough for that width. A 4000-pixel photo scaled to 1200 is already ~70% smaller.
- On Windows: Photos → Resize, or Paint → Resize → Pixels.
- On macOS: Preview → Tools → Adjust Size → set width to 1200–1500 px.
- On phone: any ‘image size’ or ‘photo compress’ app that lets you set width and JPEG quality.
JPEG vs PNG: pick the right format
Use JPEG for photos, scans, and anything with gradients. JPEG compression is designed for them and produces much smaller files. Use PNG only for graphics with flat colours and hard edges (logos, screenshots with text).
JPEG quality 70–80% is visually lossless for documents; dropping to 50–60% saves more for web sharing where perfect photo fidelity is not needed.
Building the PDF the lean way
After resizing, insert the images into Word, Google Docs, or any PDF creator at their actual size: do not drag them huge and then shrink visually; the full pixel data is still stored. Export with ‘Smallest file size’ or equivalent option if offered.
If you already combined images into a PDF, compress that PDF once with Shrinklyy rather than re-processing individual images. One pass is cleaner than several.
Quick check before you send
Open the final PDF, zoom to 100%, and look closely at the smallest text and the most detailed photo. If both are fine, you are done. If a photo looks soft, reinsert it at slightly higher quality and re-export: you still have the original sized image to adjust.
Frequently asked questions
Quick answers to the questions readers ask most about this topic.
For A4 documents, 1200–1500 pixels wide is usually ideal. It prints sharply at 150–200 DPI and keeps the PDF lean.
Resolution metadata (DPI) matters less than actual pixel count. A 4000px image tagged as 150 DPI is still 4000px. Resize the pixels: that is what determines size.
You can, and it works well. But trimming images first means you can use gentler compression on the PDF and get a cleaner result with more headroom for strict limits like 200 KB.
Try these tools
Matched to the workflow described in this guide.