Vector PDF against image PDF, and why it matters

PDF is a container, and the extension does not tell you what is inside. The same .pdf can hold a photograph of a page or the mathematical description of every line on it. For drawings, that distinction decides whether the file is useful at all.

What each one stores

Telling which one you have

1. Open the PDF and zoom to 400%. Sharp edges mean vector; visible square pixels mean an image.
2. Double-click on a label. If it can be selected, it is real text.
3. Search the document (Ctrl/Cmd + F). If the project name in the title block is found, it is vector.

Why drawings need vector

The detail stays readable

On a floor plan at 1:100, level annotations 2 mm high are nearly invisible on screen. In a vector PDF you can zoom to 800% and read them. In an image PDF, the same label is a smudge beyond the resolution it was rendered at.

Print quality follows the device

A vector PDF is drawn at the resolution of whatever prints it: 600 dpi on a laser printer, 2400 dpi on a plotter. An image PDF is limited to the resolution baked into the file, and a better device will not improve it.

File size stays sane

Storing a large sheet as a raster at readable quality means an image tens of thousands of pixels across — hundreds of megabytes. The same sheet as vector fits in a few.

How to get vector

Your source has to be vector already: a DWG, a DXF, or a PDF produced directly from CAD. Turning a photograph or a scanned sheet back into vector is a separate and laborious job. If you have the DWG or DXF, you can produce vector PDF directly.