Compressing reduces a file's size by encoding data more efficiently for storage or transfer.
Conversely, flattening merges multiple layers, annotations, or form fields into a single, non-editable layer, primarily for security and printing compatibility. While compression always shrinks files, flattening mainly secures content.
For best results, we always recommend flattening your files before uploading. This helps make sure each layer of photos, text and other elements display correctly when put through our process.
When to Use Which:
Compress: When a file is too large to send or takes up too much storage.
Flatten: When a document has complex layers, signatures, or forms that need to be locked before sharing.
We recommend using https://www.sejda.com (which is a free PDF design platform) to flatten your PDF file.
Here is the link to the 'Flatten' section of the page: https://www.sejda.com/flatten-pdf
Our customers also use Smallpdf.com for flattening if Sejda doesn't work, and for compressing their files.