Smallpdf's iPhone guide distinguishes PDF compression from the Files app's Compress command, which creates a ZIP archive. Its browser workflow uploads the PDF in Safari, applies a compression level and downloads a smaller PDF. Image-heavy scans may shrink more than simple text files.

Reduce an iPhone PDF with Actual PDF Compression

Check the compressed result before removing the original. Choose a reduction level around the required upload size and readable output, rather than assuming a smaller file always preserves the details needed by its recipient.