You may have a 5 MB upload limit and a PDF that is four or five times that size. Before running it through several compression tools, it helps to know what is actually inside the file.
The biggest savings usually come from images, but they are not the only factor. Embedded fonts, graphics and the way the PDF was created can all affect file size.
Start by checking what is inside the PDF
Scanned documents are often much larger than documents created directly from text.
A digitally created page can store text and a relatively small number of drawing instructions. A scanned page is usually stored as an image, and a high-resolution image repeated across dozens of pages adds up quickly.
The same applies to presentations with full-resolution photography, proposals full of renders and documents containing large screenshots.
A quick check is to try selecting a sentence in the PDF. If the words can be selected and searched, the file contains a text layer. If nothing can be selected, it is likely to be image-based.
This is only a useful clue, not a definitive test. Scanned PDFs can contain an OCR text layer on top of the page images.
The first thing to try: compress the images
For many large PDFs, reducing image resolution or image quality gives the best balance between file size and usability.
Done properly, this leaves the text layer intact. You can still search the document, copy text from it and preserve more of its accessibility than you would by flattening every page into an image.
The trade-off is image quality. Moderate compression may be difficult to notice on screen, while aggressive compression can make photographs, diagrams and small text inside images visibly worse.
Flattening pages is a last resort
Another option is to render each page as a single image.
This can produce a smaller file in some cases, but it changes the nature of the document. Unless OCR is added again afterwards, text is no longer searchable or selectable, and screen readers lose access to the original text structure.
That may be acceptable for a PDF that was already just a collection of scans. It is a much bigger compromise for a contract, proposal or report that began as a digital document.
Use it when reaching the size limit matters more than preserving the document's original structure.
What usually does not solve the problem
Putting the PDF in a ZIP file
PDFs already use compression internally for many types of content, so putting a PDF inside a ZIP archive often saves very little.
It also does not help when the website or form expects a PDF rather than an archive.
Removing metadata
Metadata can contain information you may want to remove for privacy reasons, but it is rarely the main reason an ordinary PDF is too large.
If you need a meaningful reduction, images, fonts and other document resources are usually more relevant.
Printing the document to a new PDF
"Print to PDF" creates a new version of the document, but it is not a predictable compression method.
Depending on the software involved, it can discard links, accessibility tags, form information or other structure. The resulting file may be smaller, but it may also be the same size or larger.
If file size is the goal, use a tool that lets you control compression directly.
There is no universal minimum file size
Page count alone does not tell you how small a PDF can become.
Two 100-page documents can have completely different file sizes depending on their images, fonts, graphics and internal structure.
If a PDF has already been optimised well, running it through another tool may produce very little improvement. In some cases the new file can even be larger than the original.
When that happens, your options are straightforward:
- keep the original if the saving is negligible;
- split the document if the receiving system allows multiple files;
- accept more aggressive image compression if meeting the limit is essential.
Always open the compressed file and inspect it before sending it. A smaller number is not useful if the document has become difficult to read.
Reduce the file without uploading it
If the PDF contains a contract, financial information, an ID scan or other sensitive material, there is another question worth asking: does the file need to leave your device at all?
Compression, merging, splitting and page reordering can all be done locally in the browser.
We built a free PDF tool that works that way. Set the maximum file size you need — 2 MB, 5 MB, 10 MB or another value — and it will try to reduce the PDF to fit.
You can choose to preserve the text layer or use a more aggressive image-based option when file size matters more than searchability.
The PDF is processed in your browser and is not uploaded to our servers. No account or email address is required.
The short version
If images are responsible for most of the file size, compress those first.
Preserve the text layer whenever searchability, copying or accessibility matters. Flatten pages into images only when you understand what will be lost and need the extra reduction.
ZIP archives and Print to PDF are poor substitutes for deliberate PDF optimisation.
And if the file is already well optimised, there may simply be very little left to remove without reducing quality.
For sensitive documents, local processing also means you can make the basic changes without sending the PDF to a remote server.
