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Choose a size limit or a quality preset
Use ToolKnit's PDF compressor when a document is too large for an upload form or attachment. Compress to a target size checks each finished PDF against your chosen maximum. Smart compression offers Low, Medium, and High presets when you do not need one specific limit.
A target is a ceiling, not an exact output size. A successful result can be smaller than the selected limit. No compression tool can make every document tiny while preserving every detail.
How to compress a PDF to 100 KB, 500 KB or 1 MB
- Add one PDF. Select a file up to 50 MB. Processing stays in your browser; the PDF is not uploaded to ToolKnit.
- Choose Compress to a target size. Pick a preset or enter a custom maximum between 50 KB and 50 MB. For example, choose 500 KB when that is the upload limit.
- Run compression. The tool adjusts JPEG quality and page resolution, then checks the encoded PDF's byte size. Processing time depends on pages, content, and your device.
- Check the result. Only a result at or below your chosen maximum is offered as a target-size download. An original that already meets the limit is kept unchanged.
- Open the downloaded PDF. Review every page, especially small text, numbers, signatures, and diagrams, before submitting it.
Check the receiving website's units. ToolKnit uses 1 KB = 1,024 bytes and 1 MB = 1,048,576 bytes. A website that means 100,000 bytes by “100 KB” has a slightly lower limit; choose a smaller target, such as 97 KB, and verify acceptance there.
What changes in the compressed PDF?
When ToolKnit rebuilds a PDF, both target-size mode and Smart compression render its pages as JPEG images inside a new PDF. This is not lossless PDF optimization or font subsetting. Page dimensions are retained, but visual detail can decrease as quality or render resolution is reduced.
- Selectable and searchable text is not retained in the rebuilt PDF.
- Working links, editable form fields, bookmarks, and accessibility tags are not retained.
- A file returned as the unchanged original keeps its existing content and features.
Keep the source PDF. If you need searchable text, editable forms, accessibility, or print-quality detail, an image-based compressed copy may not fit your task.
When a very small target cannot be reached
A long document contains many pages even after its images are compressed. Detailed scans can also need more space than a tiny upload allowance permits. ToolKnit tries a limited range of compression settings; if none meets your maximum, it shows a failure rather than offering an oversized file as a success.
Try a larger allowed limit or reduce the document's content at its source. Do not keep recompressing an already compressed copy: return to the original for each attempt. A size check confirms bytes, not readability.
Why a result can show 0% savings
In target mode, a PDF already below the maximum does not need another conversion. In Smart mode, ToolKnit also keeps the original if the rebuilt PDF would be as large or larger. A 0% result in these cases avoids making your file worse.
Check an example with your own document
Start with a non-confidential PDF containing both a photo and a paragraph of small text. Keep the original, select a 500 KB target, and compare file bytes, page count, text legibility, and text selection in the output. Then try an original already below 500 KB: it should be returned unchanged. Different documents and browsers can produce different results.
A measured example
In a local Chrome 152 check on September 16, 2026, a generated one-page document containing a detailed image and text went from 1,327,778 bytes to 478,838 bytes with a 500 KB target (512,000 bytes). The output still had one page. A separate 894-byte PDF already below the limit was returned byte-for-byte unchanged.
These are synthetic test documents, not an average compression rate or a guarantee for your file. Use your own document to check readability and whether an image-based copy is appropriate.
Frequently asked questions
Can I compress every PDF to 100 KB?
No. 100 KB is an available target, not a promise for every document. Successful downloads meet the chosen maximum; documents that cannot reach it within the tool's compression limits are reported as unsuccessful.
Is Low compression lossless?
No. Low uses the highest-quality Smart preset, but a rebuilt file still contains rendered JPEG pages. Inspect the result and keep the original.
Can I process several PDFs at once?
This compressor processes one PDF at a time, up to 50 MB. It requires no account. Processing limits apply; it is not an unlimited batch PDF service.
Does private processing mean there is no website analytics?
Your PDF contents are processed locally and are not uploaded. The website uses analytics separately; see the privacy policy for those details.
Choose the next PDF task
- Merge PDFs when you need to combine documents.
- Export PDF pages as images when you need a page image rather than a smaller PDF.
- Create a PDF from images when your source files are photos or scans.
- Compare six PDF workflows to choose the right tool.