If you are working at any size other than 100 percent, which is full-size, make certain the output percentage is indicated on the work order. If for some reason you don't have a form, include the output size as a comment within the PDF if possible. Failing that, attach a text file with your archive for output that clearly indicates at what size the file should be printed. The maximum PDF output enlargement is 400 percent.
The best way to submit a poster developed from a smaller projects such as a flyer or brochure is to recreate a new document at the proper size even though this may require editing styles. One reason this is recommended is the output operator assumes any file is output at 100% unless otherwise indicated. Another reason is that you are more likely to include photographic images at the proper resolution when working at the correct size.
The alternative is to work at a consistent scaled proportion. Any rasterized images must have sufficient resolution at the printed size. So if the document will be printed at 200 percent and 240 PPI photos are ultimately desired, images in the small document would be twice the size or 480 PPI. Scaling the photo up in Photoshop helps but it is better to locate the original or a larger version of the image and see if it has enough pixels to be printed at a larger size. Sharpening applied in a small image is grossly emphasized when enlarged. This is why it is good to have a rather large unsharpened master. After scaling and cropping a copy to the desired size, minimal sharpening can be added as the last step if required before saving as a TIFF.
Vector artwork, like that produced in Adobe Illustrator, is resolution independent, meaning it can be scaled to any size without loss of quality. Rasterized images like photos, whether they be TIFF or JPEG, are handled differently. In fact, some vector special effects and Photoshop layer styles may require verification after scaling.
For example, Adobe Illustrator offers options for rasterizing transparency effects anywhere from 300 to 1200 PPI (pixels-per-inch) when saving an EPS file. For a desktop printer or small print job, 300 or 600 PPI may look fine. But when the same image, will be scaled twice the size, vector effects may not print as smoothly. Large high-resolution poster output benefits from 1200 PPI rasterization for EPS transparency effects.