A PDF that uploads fine to Google Drive gets rejected by a government portal. A file that sails through email lands in the spam folder when sent through a recruitment platform. A document that your client's system accepted last month now triggers an error. Different platforms impose different file size limits, and they enforce them at different points in the upload process. Knowing the limits is only half the solution. Knowing how to hit a specific size target is the other half.
Generic compression reduces file size. Targeted compression reduces file size to meet a specific number. The difference matters when a platform rejects files over 10MB and your compressed PDF comes in at 11MB. You do not need to compress everything more. You need to shave off one more megabyte. This guide covers how to do that efficiently.
The table below shows common file size limits across the platforms where PDFs are most frequently uploaded or attached.
| Platform or Service | Typical File Size Limit | Enforcement | Compression Target |
|---|---|---|---|
| Gmail attachments | 25MB | Rejected at send time; no partial delivery | Under 20MB for reliable delivery with email body overhead |
| Outlook attachments | 20MB to 34MB depending on version | Rejected at send time; OneDrive link offered as fallback | Under 15MB for consistent delivery across Outlook versions |
| LinkedIn job applications | 2MB to 5MB | Rejected during upload; no partial submission saved | Under 1.5MB to leave room for the application form data |
| Government portals | 5MB to 30MB, varies by agency | Rejected at upload; some portals do not state the limit upfront | Under half the stated limit; portal overhead can consume 10-20% of the allowance |
| Recruitment platforms (Workday, Greenhouse) | 2MB to 5MB | Rejected during upload; some allow retry with a smaller file | Under 1MB; resumes and cover letters compress efficiently |
| Cloud storage (Google Drive, Dropbox) | Varies; typically 750GB+ per file for paid plans | Rarely enforced for normal documents; more relevant for video and datasets | No special target needed for typical PDFs |
Why Platform Limits Differ So Widely
Platform file size limits are not arbitrary. Email providers set limits based on their storage infrastructure and the need to keep attachment processing fast for all users. Recruitment platforms set low limits because they store millions of applicant documents and storage costs scale with volume. Government portals set limits based on their backend systems, which may be older and less capable of handling large files.
The limit is not a judgment on your document. It is an infrastructure constraint. Treat it as a specification to meet rather than an obstacle to resent. The Reduce PDF Size approach that works is precise compression, not maximum compression.
Precision Compression: Hitting a Specific Size Target
Maximum compression reduces file size as much as possible in one pass. Precision compression reduces file size to meet a specific target through iterative refinement. Start with moderate compression and check the result. If the file is still over the limit, compress again at a slightly more aggressive setting. Repeat until the file fits under the target with acceptable quality. Each iteration brings the file closer to the target without overshooting and degrading quality unnecessarily.
WukongPDF's PDF Compression tool supports this iterative approach. Each compression pass is fast enough that three or four iterations take less than a minute total. The goal is to stop at the right size, not the smallest possible size.
Which Content to Target for the Last Few Megabytes
When you are within a few megabytes of the target, switch from broad compression to targeted reduction. Images are almost always the largest remaining contributor. If the PDF contains photographs, downscaling them from 300 DPI to 150 DPI can save several megabytes with minimal visible difference on screen. Removing unused pages trims weight without affecting content quality. Stripping embedded thumbnails and preview images recovers space that serves no purpose in the final delivery.
These targeted reductions work because they affect the largest data objects in the file. Broad compression treats everything equally. Targeted reduction treats images, pages, and metadata separately and makes deeper cuts where they matter most.
Verifying Size Compliance Before Upload
Check the file size on disk, not the size reported by the compression tool. The tool reports the size after its own processing, but your operating system may report a slightly different number due to how file sizes are calculated and rounded. The platform you are uploading to uses the operating system's calculation. If the platform says the limit is 10MB and your file shows 9.9MB in File Explorer, you are likely safe. At 10.1MB, you are not.
Leave a safety margin. If the limit is 10MB, target 9MB. Platform overhead, form data, and email encoding can add a few hundred kilobytes to the transmitted size. The PDF File Size on your device is not exactly the size the platform receives. The margin protects against this discrepancy.