Normal mode versus strong mode
Normal mode re-saves the PDF with an optimized structure. Text stays selectable and searchable, and nothing visible changes. The gains are modest, often 5 to 30 percent, and they depend on how wastefully the file was written in the first place.
Strong mode re-renders each page as a compressed JPEG image and builds a new PDF from them. This can bring a 40 MB scan down to a few megabytes. The trade-off is real: text is no longer selectable or searchable, and small print may look softer. Use it for scanned documents that are already just pictures of pages.
Choosing the right mode
If the PDF came from a word processor, exported slides or a web page, try normal mode first. It is already mostly text and vector shapes, so there is little to squeeze, and strong mode would make it worse by turning crisp letters into pixels.
If the PDF came from a scanner or a phone camera app, strong mode is the one that matters. These files are just photographs of paper, so image compression is where the savings are.
A simple test: try to select a word in the PDF. If you can, the text is real, and normal mode is the one that preserves it. If you cannot, the pages are pictures and strong mode will give a much larger saving.
Mixed documents, such as a report with scanned signature pages at the back, are a case for splitting. Compress the text part in normal mode, the scanned part in strong mode, then merge the two results back into one file.
Hitting an email or portal limit
Many email providers cap attachments around 20 to 25 MB, and application portals commonly accept 2 to 5 MB. If strong mode is still too large, split the document or delete pages that do not matter, such as blank backs. Compressing the source photos before building a PDF from them with the JPG to PDF tool also helps.
Always open the result and check the pages that matter, such as signatures and figures, before sending.
Safety and limits
Your file is handled by your browser only. Password-protected or encrypted PDFs are not supported, and the maximum input size is 100 MB. Keep your original, because strong mode cannot be reversed.
Compare the sizes shown before and after. If the new file is not smaller, the tool tells you, and you can keep using the original. Strong mode works best at keeping legibility on scans made at 150 dpi or more.