How to Compress Multiple PDF Files at Once (Batch PDF Compression Guide)

Step by step: compress many PDFs in one go

1. Gather the files in one folder. It is much easier to select a batch when everything sits together. If the files come from email attachments or different downloads, move them into one place first.
2. Open Compress Multiple PDFs and click Choose PDF files. Select everything with Ctrl+A (Cmd+A on a Mac), or drag the selection from your file manager onto the page.
3. Check the list. Each file shows its size and page count. Files that are password protected or damaged are flagged before you start. Remove anything you added by mistake with its X button, and add more files with the Add more PDFs box.
4. Pick one level for the batch. Balanced is the right starting point for most work.
5. Leave Maximum compression unticked unless the batch is made of scans and the standard levels are not enough (more on that below).
6. Click Compress and wait for the progress bar.
7. Download. Download all (ZIP) saves everything as one archive. The list underneath lets you save individual files, which is handy if you only need a few of them right away.

Each output keeps its original file name with a -compressed suffix, so invoice-0423.pdf becomes invoice-0423-compressed_newkitapp.com.pdf. If two files in the batch share a name, the second gets a number added so neither overwrites the other inside the ZIP.

Choosing settings when your files are mixed

One setting for the whole batch is convenient, but it works best when the files in the batch are similar. Here is how different kinds of documents respond.

Photo-heavy documents

Brochures, product catalogs, real estate listings, and reports full of photos shrink dramatically. Their images are usually exported at print resolution, far more than any screen shows. On Balanced, a 25 MB brochure commonly drops below 3 MB with no difference visible at normal zoom. These are the files where batch compression pays off most.

Scanned documents

Scans are a special case. Every page is one large image, often stored in a format that JPEG recompression cannot improve much without visible loss, such as black and white CCITT or JBIG2 images. The standard levels may only trim them a little.

For batches of scans, tick Maximum compression. Instead of recompressing images inside the existing structure, it renders each page as a fresh JPEG at a resolution matched to your level (150 DPI for Light, 110 for Balanced, 80 for Strong) and rebuilds the PDF. A 40-page scan at 300 DPI often goes from 60 MB to around 5 MB this way. You lose selectable text, but a scan never had real text in the first place. If you need the text to be searchable afterwards, run the compressed file through OCR PDF.

Text documents exported from Word or Google Docs

Contracts, letters, CVs and reports exported straight from a word processor contain few images, so there is little to compress. The tool still rewrites the internal structure with compressed object streams, which trims a little overhead, but do not expect a 2 MB text PDF to fall to 200 KB. Most of its weight is embedded fonts, and removing fonts would break the text.

Never put these files through Maximum compression. It would turn crisp, searchable text into pictures of text, make the files harder to read on small screens, and sometimes make them larger.

Receipts and phone photos converted to PDF

Receipts snapped with a phone camera and saved as PDF are usually huge for what they contain: a 12 megapixel photo of a slip of paper. Balanced or Strong shrinks them enormously. If they will only ever be viewed on screen or filed with an accounting system, Strong is fine. If you also want them black and white for cheaper printing, Grayscale PDF removes another 20 to 40 percent.

The practical rule: split the batch by type

When results matter, sort first and run two or three smaller batches:

• Batch 1: scans, with Maximum compression on.
• Batch 2: photo-heavy documents, on Balanced.
• Batch 3: text documents, on Light or Balanced, mostly to clean up structure.

Three batches of twenty take barely longer than one batch of sixty, and each group gets the setting that suits it.

Fitting a batch under upload limits

Many batch jobs are driven by a portal or email limit rather than a wish for small files. Typical limits look like this:

• Gmail and Outlook attachments: 20 to 25 MB per email in total, but the encoding used for attachments adds about a third, so the real budget is closer to 15 to 18 MB of files.
• Job application portals: often 2 to 5 MB per document.
• Government and visa portals: frequently 1 to 2 MB per file, sometimes as low as 500 KB.
• University and scholarship systems: usually 5 to 10 MB per upload.

For a set of application documents, run the whole set on Balanced first. Then look at the list: the result shows each file's new size. Any file still over the limit can go through a second, single-file pass on Strong. That two-step approach keeps quality high on the files that fit easily and only sacrifices detail where it is needed.

If you are emailing a batch, remember the total matters as well as each file. Ten files of 3 MB each still make a 30 MB email. Either compress harder, send in two emails, or share the ZIP through a storage link instead. Our guide to PDF file size limits for email and portals lists more limits and workarounds.

Merge first or compress first?

If the end goal is one combined PDF, for example a single application packet, merge first, then compress the merged file. When several documents share the same fonts or logos, a merged file can store them once, and compressing at the end means each image is re-encoded only once.

If the end goal is a set of separate files, as with receipts that go into an accounting system one by one, batch compress the files and keep them separate. You can always merge later with Merge PDF, and merging already compressed files does not reduce their quality further.

What you should avoid is compressing, merging, and then compressing again. Every round of JPEG compression throws away a little more detail, and the second pass saves much less than the first while adding visible softness.

Common mistakes with batch compression

Compressing files that were already compressed. If a batch came from a scanner app or another online compressor, it may already be at a reasonable size. Running it again adds blur for a few percent of savings. Check the sizes in the list before you start: a 200 KB single-page PDF does not need help.

Using Strong for everything. Strong is meant for strict limits and screen viewing. For anything that might be printed, such as contracts, certificates or brochures, start on Balanced or Light and only step up when a file is still too large.

Leaving protected files in the batch. Password-protected PDFs cannot be compressed without the password. They are flagged in the list, and you should remove them, unlock them with Unlock PDF, and add them back. If they need protection afterwards, apply it again with Protect PDF once compression is done.

Deleting the originals straight away. Keep the originals until you have opened a few of the compressed copies and checked them at 100 percent zoom. If one looks too soft, you can recompress it from the original on a lighter setting.

Running huge batches on a phone. Phones have far less memory available to a browser tab than laptops. For batches of more than 20 to 30 large files on a phone, split them into smaller groups.

Why do it in the browser instead of uploading

Most online PDF compressors upload your files to a server, compress them there, and send them back. For a single brochure that might be fine. For a batch, the trade-off gets worse in every way.

Privacy. Batches tend to be the sensitive stuff: a year of bank statements, a folder of employee contracts, client invoices, medical paperwork. Uploading them means trusting a third party's storage, retention policy and security. When compression runs in your browser, the files never leave your device, so there is nothing to delete afterwards and nothing to leak.

Limits. Server-based tools have to pay for processing and bandwidth, so free plans cap the number of files per batch, the size of each file, or the number of tasks per day. A browser-based tool uses your own computer, so there is no reason for a cap.

Speed. Uploading 300 MB on a typical home connection can take longer than compressing it locally. With local processing, the only wait is the compression itself.

If you want more background on this, read Is it safe to upload PDFs to online tools? and how to compress confidential PDFs in your browser.

A worked example: a month of expense receipts

Say an accountant has 48 receipts for October. Some were scanned on an office copier at 300 DPI, some were photographed with a phone and saved as PDF, and a few are invoices exported from suppliers' systems. Together they weigh 186 MB, and the expense system accepts files up to 1 MB each.

1. Sort. The 21 copier scans go in one group, the 19 phone photos in another, and the 8 exported invoices in a third.
2. Scans: run with Maximum compression on Balanced. Each 3 to 6 MB scan comes out around 250 to 400 KB.
3. Phone photos: run on Strong without Maximum compression. Each 4 MB photo PDF drops to roughly 300 KB, because the photo inside is scaled from 4000 pixels to 1100 on the long side.
4. Exported invoices: these are already 80 to 200 KB each. Leave them as they are.
5. Result: all 48 files fit under 1 MB, the total falls from 186 MB to about 15 MB, and the whole job takes a few minutes of clicking instead of an afternoon.

Frequently asked questions

How many PDFs can I compress at once? There is no fixed limit. The practical ceiling is your device's memory, and because files are processed one at a time, most laptops handle hundreds of files per batch without trouble.

Will the file names change? Each compressed file keeps its original name with -compressed added before the extension. Files with the same name get a number so they do not collide in the ZIP.

Can I compress a whole folder? Open the folder in your file manager, select all the PDFs, and drag them onto the page. Browsers do not allow a web page to read a folder by itself, but selecting all its files gives the same result.

Does batch compression reduce quality more than single-file compression? No. Each file gets exactly the same treatment it would get on its own. The batch only automates the repetition.

Why did some files in my batch barely change? They contain few images or images that are already well compressed. Text-heavy files and files exported from another compressor have little left to remove.

Can I compress multiple PDFs on an iPhone or Android phone? Yes. Open the tool in your mobile browser, choose files from the Files app or your downloads, and save the ZIP afterwards. For large batches, use smaller groups.

A routine that works

For most batches, this short routine gets good results with very little thought:

1. Collect the files in one folder and remove anything protected.
2. Split scans from everything else.
3. Compress scans with Maximum compression on Balanced, and everything else on Balanced.
4. Check the sizes in the result list and re-run only the files that are still too large on Strong.
5. Spot-check a few files at 100 percent zoom, then delete the originals if you no longer need them.

Ready to try it? Open Compress Multiple PDFs, drop in your files, and let the batch run while you get on with something else.