Why PDF Files from Images Can Be Large
When you convert an image to PDF, the image data is embedded directly inside the PDF file. A high-resolution photo taken with a modern smartphone can easily be 8–12MB. Convert 10 of these to a single PDF without any compression and you could end up with a 100MB file — too large to email, upload to most portals, or store efficiently.
Understanding why PDFs are large helps you choose the right reduction strategy:
Method 1: Use Compression Settings at Conversion Time
The most effective way to reduce PDF size is to compress the images before or during conversion. imgs2pdf.com automatically applies light compression to images over 3MB during conversion, which reduces output file size without a visible quality drop.
For maximum compression at the source:
Method 2: Use Adobe Acrobat Compress PDF
Adobe Acrobat (paid) has the most control over PDF compression:
Acrobat can typically reduce an image-heavy PDF by 30–70% with minimal visible quality loss.
Method 3: Use Smallpdf, ILovePDF, or PDF2Go (Free Online)
Several free online tools can compress a PDF after you have created it:
These services do upload your file to their servers for processing, so avoid using them for sensitive or confidential documents.
Method 4: Use macOS Preview (Mac Only)
Mac users can reduce PDF file size using Preview's built-in Quartz filter:
This method can be overly aggressive and significantly reduce image quality. It is best for documents where readability matters more than image sharpness.
Method 5: Print to PDF with Compression (Windows)
On Windows, you can re-print a PDF to a new PDF with different compression:
This is a crude method but can work when other options are unavailable.
Choosing the Right Resolution
Resolution (DPI — dots per inch) has a direct impact on file size:
| Use case | Recommended DPI | Typical file size per page |
|---|---|---|
| Screen viewing only | 72–96 DPI | 50–150 KB |
| Email / web upload | 150 DPI | 100–300 KB |
| Standard printing | 300 DPI | 300 KB – 1 MB |
| Professional print | 600 DPI | 1–4 MB |
If your PDF will only ever be viewed on screen, 150 DPI is more than enough and will be 4x smaller than a 300 DPI equivalent.
How Much Can You Compress Without Visible Loss?
For photographic content (JPG images), compressing from 100% quality to 80% quality reduces file size by roughly 60–70% with no perceptible difference when viewed on a normal monitor. Going below 70% quality starts to introduce visible artifacts, especially in areas with gradients or fine detail.
For scanned documents (black text on white background), aggressive compression can reduce file size by 90% or more because there is very little color variation in the image — most pixels are either black or white.
Practical Example
A user has 8 JPG photos from a smartphone, each approximately 4MB, totalling 32MB. After converting to PDF:
A 4–6MB PDF is well within the 10MB attachment limit of most email services.