How this table was built
Every cell comes from one of two places: a statement on the vendor's own pricing or tool page, or a measurement made by FileConvertLab by uploading test files to the tool. The footnote on each value says which, and the date it was checked. Where a vendor publishes no figure, the cell says so instead of guessing.
Prices are shown in the currency the vendor displays and are the lowest paid plan we found; introductory discounts, regional pricing and team plans are left out. Vendors change limits without notice, so treat the dates as part of the data and check the linked page before deciding.
Where each service stands out
PDF24 is the only service in the table with no limits and no paid plan at all, financed by ads, and it ships a desktop app. Adobe Acrobat is the reference implementation of the format and the strongest choice for enterprise features, at the highest price. Smallpdf and iLovePDF offer the broadest tool catalogues and mobile apps, with the tightest free tiers of the group. Sejda's free tier is unusually generous on file size and it is the only one here with a visual PDF editor at no cost.
FileConvertLab converts up to 100 MB without an account, publishes its usage statistics and starts paid plans at the lowest price in the table, but its free tier caps documents at 20 pages until you register. The PDF format guide explains what the converters are working with.