Picking a format
Plain numbers (1, 2, 3) are clean and take little space. The Page 1 of N format tells readers how long the document is, which is helpful for contracts and reports where a missing page matters. If someone prints your file and drops a sheet, they will notice at once.
For short documents, plain numbers are enough. For anything legal or financial, use the long format.
Legal and academic documents sometimes require a number on every page, including the first. Some style guides skip the cover and start numbering on the second page, so check the rules for your submission before you apply the numbers.
Position and start number
Bottom center is the safe default for most documents. Bottom right suits double sided printing and reports. Top positions are useful if a footer is already occupied by a company address or a confidentiality notice.
The start number lets you begin somewhere other than 1. If your PDF is the second part of a larger report whose first part ended on page 24, start at 25. Page numbers are counted from the first page of the file, so a cover sheet counts as a page unless you split it off first.
Mirror positions for two-sided printing are not offered, so choose a centered number if the document will be bound with a spine on either side. A centered footer looks right on both left and right pages.
Avoiding clashes with existing content
The numbers are drawn on top of each page. Scanned pages with content close to the edge or an existing footer may overlap with them. Look at the pages after applying the numbers, and try another position if anything collides.
For documents with a cover page, a good routine is to split off the cover, number the rest starting at 1, then merge them back together.
If your document already has page numbers in the footer, such as a report exported with its own numbering, do not add another set. The two will overlap or look like an error. Use top placement only if the top margin is clear.
File notes
Existing content, text selection and links are kept. Files can be up to 100 MB, and encrypted PDFs are not supported. The processing happens in your browser, so contracts and personal files are not uploaded.
Because the numbers are added as ordinary text on the page, they look the same in every viewer. If you apply numbers twice by mistake, start again from your original file.