How to compress a PDF for an online form: getting under 100 KB, 200 KB, 500 KB or 1 MB

An upload limit is a budget of bytes, and in a scanned document nearly all of those bytes are page images. Divide the limit by the number of pages and you know what each page can spend. One A4 page in 100 KB stays easy to read. Ten pages in 100 KB get 10 KB each, which pushes the resolution so low that small print breaks up. So try lossless compression first, then let the pages be re-encoded as smaller images, and if the per-page budget is still too thin, split the file or rescan it. The size-targeted tools on this site, such as Compress PDF to 200 KB, do the first two steps on your device and tell you which one they needed.

What actually makes a PDF large

• Text is cheap. A page of 3,000 characters is about 3,000 bytes of text before compression, and fonts are stored once for the whole document.
• Images are expensive. An A4 page at 150 DPI is 1,240 × 1,754 pixels, about 2.17 million of them. Stored raw at three bytes per pixel, that is 6.52 MB for one page. At 300 DPI it is 2,480 × 3,508 pixels and 26.1 MB. JPEG compression cuts this a great deal, but the pixel count sets the scale.
• Scans and phone photos are images of pages. A scanned PDF holds no text, only one picture per page. Colour, paper texture, shadows and camera noise all cost bytes.

To see which kind you have, try to select a single word. If you can, it is a text PDF and lossless compression may be enough. If you cannot, every page is a picture.

The limits forms set, in their own words

These examples are from official notices, read on 13 October 2026 (UPSC re-checked on 21 October 2026, after its move to upsconline.nic.in).

Form	Document	Stated limit
JEE (Main) 2026, National Testing Agency	Class 10 certificate or marks-sheet; disability certificate	PDF, 50 kb to 300 kb
NEET (UG) 2026, National Testing Agency	Category certificate, Class X certificate and marks-sheet, address proof and similar	PDF, 50 kb to 300 kb
IBPS CRP PO/MT-XVI	Class 10 certificate	PDF, A4 page size, not exceeding 500 KB
PAN application with scanned images (Protean)	Supporting documents	PDF/A or JPEG, 200 DPI, black and white, maximum 300 KB per page
UPSC, new portal upsconline.nic.in	Matriculation certificate, caste certificate, disability certificate and similar	PDF, 50 KB to 300 KB

Two details are easy to miss. Three of the five set a minimum as well as a maximum, so a file squeezed far below the floor fails too. And the limit can be per file or per page: Protean counts 300 KB for each page, the others count the whole file. Both NTA bulletins require uploads to be “clearly legible”, and IBPS warns that an unclear or smudged document may get the application rejected.

How compression works

1. Lossless clean-up. The file is rebuilt: internal objects are packed into compressed streams, existing streams are recompressed at the highest level, and unused resources are dropped. Nothing on any page changes. It helps scans very little, because their page images are already compressed.
2. Lower resolution. Each page is rendered again with fewer pixels. Size falls roughly with the square of the resolution: going from 150 to 100 DPI leaves 44% of the pixels, and 72 DPI leaves 23%.
3. Lower JPEG quality. The encoder keeps less fine detail per pixel, and text edges show it first.

The site’s compress-to-a-size pages apply these in a fixed order:

• A file already at or under the target is returned unchanged.
• A lossless pass runs next. If that alone reaches the target, your text stays selectable.
• Otherwise, with If needed, convert pages to images to reach the size ticked, every page is rendered at 150 DPI and encoded as a JPEG at the lowest quality the tool allows (35% at 72 DPI and above, 15% below that). If that is still too big, the tool drops to a lower step from a fixed list: 150, 120, 100, 85, 72, 60, 50, 42, 36, 30 and 24 DPI.
• Once the lowest quality fits, it raises the quality (up to 85%) until the result is within 10% of the target, and keeps the largest result that fits.

The step is chosen from the measured size. If the first attempt at 150 DPI comes to 400 KB against a 100 KB target, the tool computes 150 × √(100 ÷ 400) × 0.95 = 71.25 and takes the next step at or below that: 60 DPI.

The target is counted at 1,000 bytes per KB, so “100 KB” means 100,000 bytes. A portal that counts 1,024 bytes to the KB sees 97.66 KB, so the file passes either way. The tool shows sizes the same way, with 1,024 bytes to the KB as Windows does, so a file right at the target reads about 97.7 KB. Once pages become images, text is no longer selectable and links and form fields are gone. The tool warns you when that happens. Keep your original.

Bytes per page: what to expect at each limit

This table is arithmetic, not a test result. It divides each target by the page count, then by the pixels in an A4 page. “Bits per pixel” is the budget the JPEG encoder gets.

Target	Pages	Per page	Bits per pixel at 150 DPI	At 100 DPI	At 72 DPI	Highest step with 0.5 bits per pixel
100 KB	1	100 KB	0.37	0.83	1.60	120 DPI
100 KB	10	10 KB	0.04	0.08	0.16	36 DPI
200 KB	1	200 KB	0.74	1.66	3.19	150 DPI
200 KB	10	20 KB	0.07	0.17	0.32	50 DPI
300 KB	1	300 KB	1.10	2.48	4.79	150 DPI
300 KB	10	30 KB	0.11	0.25	0.48	60 DPI
500 KB	1	500 KB	1.84	4.14	7.98	150 DPI
500 KB	10	50 KB	0.18	0.41	0.80	85 DPI
1 MB	1	1 MB	3.68	8.28	15.97	150 DPI
1 MB	10	100 KB	0.37	0.83	1.60	120 DPI

The paper that introduced JPEG gives a guideline for colour photographs: 0.25 to 0.5 bits per pixel is “moderate to good quality”, 0.5 to 0.75 is “good to very good”, 0.75 to 1.5 is “excellent”, and 1.5 to 2.0 is “usually indistinguishable from the original”. A scanned form is not a typical photograph: blank paper costs few bits and sharp letter edges cost many, so treat the bands as a rough guide.

Resolution matters separately from quality. A line of 10-point type is about 21 pixels tall at 150 DPI, 14 at 100 DPI, 10 at 72 DPI, 7 at 50 DPI and 5 at 36 DPI.

Put together:

• One page is comfortable at every common limit: even 100 KB leaves 0.37 bits per pixel at 150 DPI, and ten pages in 1 MB get the same budget.
• Ten pages in 500 KB is 50 KB a page. Half a bit per pixel is reached at 85 DPI, where a 10-point line is about 12 pixels tall.
• Ten pages in 100 KB or 200 KB is 10 KB or 20 KB a page. Half a bit per pixel is only reached at 36 or 50 DPI, where body text is 5 to 7 pixels tall. Small print is unlikely to stay “clearly legible”. Change the input instead.

When to split, rescan or change the scan settings

• Split by document. Forms such as the NTA ones give each certificate its own upload slot and limit. Upload them separately instead of merging everything. The PDF Splitter cuts a file By ranges, Every page or Every N pages.
• Rescan with plainer settings. IBPS tells applicants to adjust the scanner’s “DPI resolution, no. of colours” when a file is too big, and Protean asks for 200 DPI black and white. A greyscale scan starts from one byte per pixel instead of three. In the compress tools, Greyscale (smaller for text documents) converts the rendered pages to greyscale for the same reason. It keeps shades of grey; it is not 1-bit black and white.
• Photograph it better. With a phone, lay the page flat in even light, crop to the paper’s edge, then use JPG to PDF.
• Under a minimum? Compression cannot help. Rescan at a higher resolution or in colour.

Step by step with the tools

1. Read the limit in the official notice. Note whether it is per file or per page and whether there is a minimum.
2. Open the page for your limit: 100 KB, 200 KB, 300 KB, 500 KB or 1 MB. The Target size box is in KB and can be edited, so a 150 KB limit needs no separate page.
3. Choose your PDF. It is processed in your browser, not uploaded.
4. Leave If needed, convert pages to images to reach the size ticked for scans. Untick it to keep a text PDF selectable.
5. Press the Compress to… button. The summary shows the original size, the new size and the target. The Method line shows whether the result is a lossless rebuild or pages as images, and at what DPI and quality.
6. Open the result at 100% zoom and read the smallest print, the numbers, the seal and the signature. If you cannot read them, neither can the person checking your application.
7. If the target cannot be reached, the tool reports the smallest size it achieved. Split the file or pick a larger target.

When there is no fixed limit, the PDF Compressor offers Lossless, Balanced (150 DPI), Strong (110 DPI) and Extreme (72 DPI) instead of a target.

How to check this yourself

• Per-page budget: limit in bytes ÷ number of pages. 300 KB over 4 pages is 75 KB a page.
• Pixels in a page: A4 is 8.27 × 11.69 inches; multiply each by the DPI. At 100 DPI that is 827 × 1,169 = 966,763 pixels.
• Bits per pixel: bytes per page × 8 ÷ pixels. 75,000 × 8 ÷ 966,763 = 0.62.

The pixel sizes, byte targets and the worked resolution step come from the compress tool’s own functions. The tools cannot keep text selectable once pages become images, cannot make ten dense pages legible at 10 KB each, and cannot promise that a portal will accept the file. Very large PDFs can run out of memory in a browser tab.

Related tools

• Compress PDF to 100 KB, 200 KB, 300 KB, 500 KB or 1 MB.
• PDF Compressor: lossless or preset strengths, no target.
• PDF Splitter and JPG to PDF.

Portal limits are quoted from the official notices listed below, read on 13 October 2026. Confirm the current figure before you upload.