A smaller PDF is only useful if the recipient can still read and use it. Start with the destination’s actual file-size limit, keep your original, and check the downloaded result. This walkthrough describes the controls in CommandPDF’s Compress PDF tool; it does not promise a particular percentage saving.
Set a target before processing
Check the email service or upload portal you are sending to. The recipient’s organization may impose a different limit from yours, and several attachments may share one limit. Mail encoding can also increase the size of a message, so do not aim exactly at the advertised maximum.
For example, if a portal explicitly accepts one file below 5,000,000 bytes, a 5,100,000-byte PDF is too large even if your computer rounds both sizes to “5 MB.” Compare the actual output bytes with the portal’s definition of its limit. These numbers illustrate the calculation; they are not measured compression results.
Pick the algorithm for the document
Add the PDF to the tool to reveal the options. CommandPDF offers three algorithms:
- Standard rewrites the PDF structure and, if Optimize embedded images is enabled, attempts an additional image-optimization pass. If that extra processing engine fails to load, the processor can return the structure-only result. A successful download therefore does not always mean images were recompressed.
- Condense optimizes embedded images and cleans the document structure in one pass. It does not deliberately render every page as an image, but it is not lossless: the quality preset can change embedded images. Check fields, bookmarks and other features in the output.
- Photon renders pages as images. Consider it for an image-only delivery copy, not for a document that must retain selectable text, editable forms or links. Keep the source separately.
Read “quality” as output quality
The selector is labelled Compression Quality. Its labels do not mean compression strength:
- Low favors a smaller file at the expense of image detail.
- Medium is the middle quality preset.
- High and Maximum favor image quality; the result can be larger.
Those presets matter to Standard’s image pass and to Condense. They are not a uniform setting across all algorithms. Condense also uses the quality preset for its image optimization, while Photon has its own Output DPI slider. A higher Photon DPI creates more pixels per page, usually using more memory and producing a larger file.
The Remove metadata option is a separate choice. Clearing title or author information is not the same as redacting document contents, and it is not a reliable way to achieve a large size reduction.
Check the result before attaching it
After compression, download the PDF and open that downloaded file, rather than inspecting only the source preview.
- Compare the file’s byte size with your target. If it grew, keep the original or try a different mode.
- Check the page count and inspect the first and last pages.
- Zoom in on the smallest text, a fine line, and a detailed image. Check barcodes or QR codes with the reader that will actually use them.
- Search for a phrase you know was selectable in the original. With Photon, loss of the original text layer is expected.
- If there are forms, links or bookmarks, try them. For signed documents, retain the signed original; a rewritten file should not be assumed to preserve signature validity.
A scanned page can already lack a text layer before compression. Compare source and output so you do not attribute that existing limitation to the compressor.
If the result is still too large
Remove genuinely unnecessary pages with Delete Pages or create separate parts with Split PDF, if the recipient accepts several files. Splitting into equal page counts will not produce equal byte sizes: a page containing a photograph can outweigh many text pages.
Avoid repeatedly lowering quality on the only copy. Return to the original for each comparison, and stop when the result meets both the size requirement and the readability requirement. If it cannot meet both, use a delivery method the recipient accepts instead of sending an unreadable PDF.
For a deeper explanation of the processing paths, see how CommandPDF compression changes a PDF.