Preview is the PDF editor you already have

People install a PDF editor for one job, usually combining two documents, and then keep paying for it. Preview covers most of that ground already, and it never asks for an account.

Merge documents

Open the first PDF, then drag the second one onto its sidebar. If the sidebar is hidden, choose View > Thumbnails. The pages appear as thumbnails in the order you dropped them, and you can drag individual pages to rearrange.

Saving writes the merged file. File > Duplicate first if you want to keep the original untouched, because Preview saves in place.

Split and extract

Select the pages you want in the thumbnail sidebar and press Delete to remove them, or drag the selection out to the Desktop to create a new PDF containing just those pages. Dragging a single thumbnail out gives you a one-page file.

This is also the fastest way to pull a signature page, a receipt or one chapter out of a long document.

Sign it

Open the Markup toolbar (View > Show Markup Toolbar), click the signature icon and choose Create Signature. You can sign with the trackpad, with the camera using a sheet of paper, or with an iPhone or iPad if it is nearby and signed into the same Apple account. Saved signatures stay in the list.

A signature placed this way is an image on the page, not a cryptographic signature. For contracts that need real verification, use the signing service the other side asked for.

Shrink the file

File > Export, then choose Quartz Filter > Reduce File Size. A scanned 20-megabyte document often drops to two or three megabytes. The filter recompresses images, so text gets slightly softer and fine print can suffer.

Keep the original. Export is a one-way operation, and there is no undo once the compressed file replaces the source.

Fill in a form

Many PDFs with fields are recognised automatically: click a field and type. For flat forms made of lines and boxes, use the Text tool from the Markup toolbar, set the font size small, and place the text directly. It looks hand-made because it is, which is usually acceptable for internal paperwork and rarely acceptable for anything official.

What Preview will not do

It will not edit the text of a PDF. If the document was not created with editable fields, there is no layer to edit, only pixels and positioning. It also will not compare two versions, redact text securely, or assemble a table of contents. Those jobs need a real editor, and that is the point where paying makes sense.