Reduce PDF Size Without Uploading It
Four quality levels and a target size, none behind a paid tier. The document is analysed and rewritten on this device.
PDF tooling by OnlinePCApps since 2013
Three Limits That Force a Smaller PDF
Each is a fixed threshold imposed elsewhere rather than a defect in the document.
Attachment Limits
Gmail and Outlook reject attachments above roughly 25 MB. A scanned contract or a slide deck exported to PDF passes that figure without difficulty.
Fixed Ceilings on Submission Portals
Government portals, job applications, visa forms and academic submissions routinely specify an exact figure: 100 KB, 200 KB, 500 KB or 1 MB, enforced by rejection rather than a warning.
Storage and Distribution
Document archives and shared drives accumulate invoices and scans held at capture resolution rather than reading resolution.
Three Steps to a Smaller PDF
Add the Document
Choose the document. The browser opens it from disk and examines its contents.
Choose a Level or a Target
Pick a quality level, or state a target size and let the settings resolve towards it.
Compare and Save
Original and compressed sizes appear side by side. Nothing is written to disk until the result is accepted.
Local Compression vs Server-Side Compressors
The established compressors transfer the document, process it remotely and apply a retention timer. Several also impose a daily task cap and reserve their stronger levels for a paid tier.
| Property | This page This page Runs on local hardware | A typical server-side compressor Sends the document to a server |
|---|---|---|
| Compression levels at no cost | All four | Basic only, 20 to 40 percent |
| Target size setting | Supported | Rarely offered anywhere |
| Page count limit | None | 200 pages on some free tiers |
| Where the rewrite happens | This machine | A remote datacentre |
| Runs allowed per period | Unmetered | Two or three per day or hour |
| Largest file accepted | Whatever memory allows | 10 MB to 100 MB by provider |
| Copy held afterwards | None exists | Purged after one to twenty-four hours |
| Confidential material | No restriction | Subject to their policy |
| Effect of geography | None | Throughput falls with distance |
That describes how the category generally operates and singles out no particular service.
The PDF File Is Never Transmitted
Deletion timers are the standard reassurance here. One hour is typical, and the guarantee extends only as far as the operator's practices allow.
No timer applies where no document arrives. There is no endpoint capable of receiving a document and nothing of ours executes remotely. Open the browser developer tools, watch the network panel during a run and it stays empty throughout.
→ external requests ....... 0
→ source document ....... 0 requests
What Compression Removes and Rewrites
PDF compression is the process of rewriting a document so that it occupies less space: images are resampled and re-encoded, embedded fonts are reduced to the glyphs in use, and redundant objects are removed. It is usually presented as a slider with no account of what is being discarded. The table sets out each element, what happens to it and where the reduction actually comes from.
| Part | Header | What it holds |
|---|---|---|
| Colour images | downsampled and re-encoded | Resolution is reduced to the chosen target in dots per inch, then the image is re-encoded as JPEG. This accounts for most of the reduction in a scanned document. |
| Greyscale images | downsampled and re-encoded | Handled the same way as colour, at the same target resolution. Scans of printed text sit here rather than in the colour path. |
| Monochrome images | downsampled only | Bitonal scans are resampled but kept in a lossless CCITT or JBIG2 encoding, because JPEG artefacts are conspicuous on line art. |
| Image resolution | 300, 150, 96 or 72 dpi | Print quality keeps 300, standard drops to 150, screen uses 96 and maximum compression uses 72. Anything above the target is discarded. |
| Embedded fonts | subset | Only the glyphs the document actually uses are retained. A font embedded whole can carry thousands of unused characters. |
| Duplicate objects | merged | Deduplication means a logo repeated on forty pages is stored once and referenced forty times rather than embedded forty times. |
| Unused objects | discarded | Orphaned dictionary entries left by earlier edits are removed and the cross-reference table is rebuilt. These accumulate quietly through repeated saves. |
| Page thumbnails | removed | Cached preview images are regenerated by any reader on demand, so storing them adds size for nothing. |
| Document metadata | retained | Title, author and keyword fields are kept. They occupy a negligible amount of space and removing them serves no purpose. |
| Text content | untouched | Text lives in the content stream as drawing instructions rather than pixels and is already compact. It is never rasterised or degraded. |
| Vector artwork | untouched | Line art, charts and logos drawn as vectors stay vector. Converting them to images would increase size, not reduce it. |
| Form fields | retained | AcroForm fields and their values survive compression, so a filled form stays fillable. |
Where the behaviour is defined
ISO maintains PDF as an open standard. Compression reaches into the image dictionaries, the font descriptors and the object table, all of which the sources below define.
Object structure is described in the PDF specification, , which defines the indirect references that allow a repeated logo to be stored once.
Which PDF Files Actually Shrink
Results vary by an order of magnitude depending on the input. The four cases below cover almost every document brought to a compressor.
Scanned Documents
Photographic Content
Text-Only Documents
Already Optimised Files
Compress Before Merging
Note that one pass and smaller inputs produce a better result than compressing a combined file afterwards, because each source is optimised at its own resolution.
Encrypted and Signed Files
Note that a password and a signature both block the operation for different reasons: one prevents reading, the other cannot survive a rewrite.
Where PDF Compression Exceeds the Browser
Browser processing is bounded by two things: how much memory is available and the lack of direct disk access.
Where the Desktop Build Fits
Each page image is decoded, resampled and re-encoded in memory. A short document presents no difficulty. A scanned book of several hundred pages does, and a handset reaches that point long before a laptop.
Working page by page straight off the disk is what the desktop build does, and that removes the memory question.
Nothing reaches the network once installed, which suits controlled estates and offline workstations.
Pages are read from disk one at a time instead of being held together, so length stops mattering.
Apply one resolution target across a directory in a single pass.
Whole directories handled at a single resolution target, beyond what one tab can hold.
Store a level and a target, then apply the same settings to future documents.
Requires no network access at all once set up.
PDF Compression Questions
Other Document Utilities
Each works the same way: the device does the processing.
Who Maintains This PDF Compressor
Reduce a PDF Without Transferring It
Nothing installed, nothing registered and nothing sent. All four quality levels cost nothing.