Can I change text in a tiff using Illustrator?

Yes you can but not directly, I use FontForge as a bridge to Illustrator. Download FontForge (if you're on a mac you'll need to be running X11, FontForge will run under Quartz - the application menu will run under the Quartz menu). Open the desired .TTF file and it will load into FontForge. For me I've had to select the individual font which opens in a design window. From here you can choose to EXPORT and save in any of the following AI friendly formats: EPS, SVG, PDF, etc. It seems to be a one at a time process but I've only needed it for a symbols file to manipulate one or two.  I've had to simplify the paths in a few instances but that based on initial files.

People tell me I have to convert the drawings, or at least the text, to vector graphics.

No, no, no.

First, TIFF is a raster image format. It contains no text. It only contains pixels. So when you say your TIFF image "contains text", all you are really saying is that it has some arrangements of pixels that look like letters.

Second, vector graphics are just shapes defined mathematically. Yes, the character shapes contained in (most) fonts are vector graphics. But that's not all there is to making them text. So when one says that "text is vector", all one is really saying is that fonts contain vector paths that look like letters. But just having vector paths that are shaped like letters is not the same as having editable text.

Actual text is an object into which you can type using your keyboard to cause your operating system to retrieve and display from the font file the particular vector path that is shaped like the letter that corresponds to the key you press. So there's much more to an actual text object than just the image on your screen that looks like the characters.

There are optical character recognition (OCR) programs which try to programmatically "recognize" the arrangements of adjacent pixels in a raster image as text characters, and then create actual text objects containing those characters. OCR is far from perfect and is dependent upon good-quality raster images. Illustrator does not contain any OCR feature.

Whomever is telling you otherwise is confusing autotracing with OCR. Autotracing is another kind of program that merely tries to draw vector paths around areas of same-colored pixels. So although you can use an autotracing program to create vector paths that are similar in shape to the clumps of pixels that you are calling "text" in your image, the result will no more be actual text that you can edit than is the raster bitmap you started with.

Acrobat Pro, on the other hand, does have a built-in OCR feature. And, Acrobat Pro can also (at least try to) export a PDF as a Word file. So you may have some success with that. But don't expect miracles. How successful you are in this attempt highly depends on the quality of the original raster image. The resulting Word document is often not at all built the way (number and arrangement of objects) you would actually build it from scratch in Word. So how usefully-editable the resulting Word document is, is dependent upon the details of the specific case.

JET

TIFF is a bitmap format, and Illustrator cannot edit bitmaps. Use Photoshop, or the closest available analog. Ask in the Photoshop forum how to do your task.

(There are ways to *change* TIFFs with Illustrator -- paste a rectangle over the old text, type in the new one, and export to TIFF again -- but that is not the best, or even a 'good' way. Compare it to using a screwdriver to hit nails with.)